Remain still believes its best hope is to shout about the potential downsides to the economy of leaving the EU - but the conduct of the campaign has damaged George Osborne's reputation among his colleagues.
"Brexit...the upcoming UK decision is something we discussed and I think it's fair to say that it was one of the factors that factored into today's decisions," said Ms Yellen.
"Clearly this is a very important decision for the United Kingdom and for Europe. It is a decision that could have consequences for economic and financial conditions in global financial markets.
"If it does so it could have consequences in turn for the US economic outlook that would be a factor in deciding on the appropriate path of policy. It is certainly one of the uncertainties that we discussed and that factored into today's decision."
Reality Check
Would there have to be emergency Brexit tax rises?
BBCCopyright: BBC
The claim: If there was a vote to leave the EU there would have to be an emergency budget.
Reality Check verdict: There is no legal requirement to have an emergency budget but the Chancellor could have one if he wanted to make immediate changes to tax rates or spending cuts.
Despite the Fed not alluding to the UK referendum on EU membership on 23 June in its formal statement today, chairman Janet Yellen has now been asked about the issue in her media conference.
She says that the forthcoming vote was one of the reasons for leaving rates unchanged, and that a Brexit vote to leave the EU could have consequences for the US economy and financial conditions.
She is basically repeating what she said last week, when Ms Yellen warned an EU exit could have "significant economic repercussions".
Econonic times they-are-a-changing
The WSJ tweets the Fed statement now and then...
US markets ahead after Fed decision
Wall Street indexes were up after the Fed decision, the Dow by 0.37%, S&P by 0.36%, and Nasdaq by 0.36%.
Investors in Europe, the US and Asia have been becoming more nervous ahead of the UK vote on 23 June on whether to leave the EU.
Fed monitors global conditions but not EU poll
The Fed also said that it was closely watching global economic and financial developments.
But it made no reference to the vote in the UK next week about whether the UK should exit the European Union.
Uncertainty around which way that vote will go is credited with creating volatility in markets in Europe and further afield.
Fed forecasts now less optimistic
Getty ImagesCopyright: Getty Images
Federal Reserve officials are less optimistic about the economy's growth this year and next, compared with three months ago.
They now expect growth to be 2% this year and next, down from previous forecasts of 2.2% this year and 2.1% in 2017.
They also expect 2% growth in 2018, the same as in March. Their unemployment rate forecasts are little changed, at 4.7% at the end of this year, the same as it is now.
The Fed projects it will be 4.6% next year and remain at that level in 2018.
The Fed on US economic conditions
Quote Message: The Committee expects that economic conditions will evolve in a manner that will warrant only gradual increases in the federal funds rate; the federal funds rate is likely to remain, for some time, below levels that are expected to prevail in the longer run. However, the actual path of the federal funds rate will depend on the economic outlook as informed by incoming data. from Federal Reserve statement
The Committee expects that economic conditions will evolve in a manner that will warrant only gradual increases in the federal funds rate; the federal funds rate is likely to remain, for some time, below levels that are expected to prevail in the longer run. However, the actual path of the federal funds rate will depend on the economic outlook as informed by incoming data.
Fed sees 'slower path of future rate hikes'
The Federal Reserve kept interest rates unchanged on Wednesday and indicated it still planned two rate increases this year.
it added that it sees a slower path of future rate hikes, with roughly three per year starting in 2017.
BreakingUS Fed keeps rates on hold
The US Federal Reserve has said it will keep interest rates at between 0.25% and 0.5%.
The bank last raised rates in December.
Fenland tractors in vogue around the globe
BBC World Service tweets....
Flatlining...
Knight Frank's Grainne Gilmore tweets a reminder of the failure to increase the number of houses being built in England.
Quote Message: "What was quite clear was that he was not being used to being questioned. Quite reasonable questions asked with some courtesy he took offence at. from Iain Wright MP for Hartlepool
"What was quite clear was that he was not being used to being questioned. Quite reasonable questions asked with some courtesy he took offence at.
GettyCopyright: Getty
Sir Philip Green accused Labour MP Iain Wright of being rude to him with his line of questioning earlier this afternoon.
Here are Mr Wright's impressions of Sir Philip's evidence, given to BBC Business Online's Jamie Robertson.
"One of the things that really struck us was the ability of him to have quite vivid recollection of detail such as where that seven million pounds went but in terms of ten years of pension schemes, which went from surplus to deficit, he didn’t know anything, and we were trying to push him on that - that curious mix, that contradiction between knowing the detail and knowing nothing at all is something we really want to push."
And as for his own style of questioning, which inflamed the retailer at times, Mr Wright said this: "What was quite clear was that he was not being used to being questioned. Quite reasonable questions asked with some courtesy he took offence at."
Live Reporting
Bill Wilson
All times stated are UK
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Wall Street closes down for fifth session in a row
Wall Street fell for the fifth session running on Wednesday after the Federal Reserve left US interest rates unchanged.
Meanwhile, investors remained cautious in light of the forthcoming referendum in the UK on 23 June about whether to leave the EU.
At close the Dow Jones was down 0.20% at 17, 640.17, the S&P was behind by 0.18% at 2071.50, and the Nasdaq lost 0.18% at 4, 834.93.
Transcript of Yellen opening statement
The Federal Reserve tweets...
'Smart guy, stupid move'
By Laura Kuenssberg
Political editor
Remain still believes its best hope is to shout about the potential downsides to the economy of leaving the EU - but the conduct of the campaign has damaged George Osborne's reputation among his colleagues.
Read moreFed Funds projections from June meeting
The FT tweets....
Yellen quotes on a possible Brexit vote
"Brexit...the upcoming UK decision is something we discussed and I think it's fair to say that it was one of the factors that factored into today's decisions," said Ms Yellen.
"Clearly this is a very important decision for the United Kingdom and for Europe. It is a decision that could have consequences for economic and financial conditions in global financial markets.
"If it does so it could have consequences in turn for the US economic outlook that would be a factor in deciding on the appropriate path of policy. It is certainly one of the uncertainties that we discussed and that factored into today's decision."
Reality Check
Would there have to be emergency Brexit tax rises?
The claim: If there was a vote to leave the EU there would have to be an emergency budget.
Reality Check verdict: There is no legal requirement to have an emergency budget but the Chancellor could have one if he wanted to make immediate changes to tax rates or spending cuts.
Read the full Reality Check here.
Fed's Yellen on the Brexit factor
Despite the Fed not alluding to the UK referendum on EU membership on 23 June in its formal statement today, chairman Janet Yellen has now been asked about the issue in her media conference.
She says that the forthcoming vote was one of the reasons for leaving rates unchanged, and that a Brexit vote to leave the EU could have consequences for the US economy and financial conditions.
She is basically repeating what she said last week, when Ms Yellen warned an EU exit could have "significant economic repercussions".
Econonic times they-are-a-changing
The WSJ tweets the Fed statement now and then...
US markets ahead after Fed decision
Wall Street indexes were up after the Fed decision, the Dow by 0.37%, S&P by 0.36%, and Nasdaq by 0.36%.
Investors in Europe, the US and Asia have been becoming more nervous ahead of the UK vote on 23 June on whether to leave the EU.
Fed monitors global conditions but not EU poll
The Fed also said that it was closely watching global economic and financial developments.
But it made no reference to the vote in the UK next week about whether the UK should exit the European Union.
Uncertainty around which way that vote will go is credited with creating volatility in markets in Europe and further afield.
Fed forecasts now less optimistic
Federal Reserve officials are less optimistic about the economy's growth this year and next, compared with three months ago.
They now expect growth to be 2% this year and next, down from previous forecasts of 2.2% this year and 2.1% in 2017.
They also expect 2% growth in 2018, the same as in March. Their unemployment rate forecasts are little changed, at 4.7% at the end of this year, the same as it is now.
The Fed projects it will be 4.6% next year and remain at that level in 2018.
The Fed on US economic conditions
Fed sees 'slower path of future rate hikes'
The Federal Reserve kept interest rates unchanged on Wednesday and indicated it still planned two rate increases this year.
it added that it sees a slower path of future rate hikes, with roughly three per year starting in 2017.
BreakingUS Fed keeps rates on hold
The US Federal Reserve has said it will keep interest rates at between 0.25% and 0.5%.
The bank last raised rates in December.
Fenland tractors in vogue around the globe
BBC World Service tweets....
Flatlining...
Knight Frank's Grainne Gilmore tweets a reminder of the failure to increase the number of houses being built in England.
Which US state shares your country's GDP?
Business Insider tweets....
Clash of Clans maker 'in $9bn takeover'
And in a spot of non-BHS news, the Wall Street Journal reports:
Sir Philip Green 'not used to being quizzed'
Sir Philip Green accused Labour MP Iain Wright of being rude to him with his line of questioning earlier this afternoon.
Here are Mr Wright's impressions of Sir Philip's evidence, given to BBC Business Online's Jamie Robertson.
"One of the things that really struck us was the ability of him to have quite vivid recollection of detail such as where that seven million pounds went but in terms of ten years of pension schemes, which went from surplus to deficit, he didn’t know anything, and we were trying to push him on that - that curious mix, that contradiction between knowing the detail and knowing nothing at all is something we really want to push."
And as for his own style of questioning, which inflamed the retailer at times, Mr Wright said this: "What was quite clear was that he was not being used to being questioned. Quite reasonable questions asked with some courtesy he took offence at."