Most opinion polls show voters are split with a large number of people as yet undecided.
Obama is due to attend a technology fair in Germany in late April and a source told the Independent on Sunday he would visit the British capital around that time.
"It would be pretty shocking if he didn`t ask voters to stay in the EU," the source was quoted as saying.
The White House declined to comment and Prime Minister David Cameron`s office did not offer an immediate comment when contacted by Reuters.
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