14 March 2011 Last updated at 19:35 ET
Mr Aristide was forced into exile in 2004
But he said a return before the election could be "destabilising".
A spokesman for Mr Aristide said last Friday that he would return from South Africa "in a few days" but insisted the move was not related to the vote.
Election US state department spokesman Mark Toner said that for Mr Aristide to return this week "could only be seen as a conscious choice to impact Haiti's elections".
"We would urge former President Aristide to delay his return until after the electoral process has concluded, to permit the Haitian people to cast their ballots in a peaceful atmosphere," he added.
In response, Mr Aristide's lawyer in Miami said the former president was concerned that he might lose his chance to return to Haiti once a new president was in place.
Speculation that Mr Aristide would attempt to come back to Haiti has grown since the surprise return in January of another former president, Jean-Claude "Baby Doc" Duvalier, after 25 years in exile.
Mr Aristide's lawyer collected a Haitian passport for him last month, but said the former president wanted to dedicate himself to education not politics.
Run-off vote Mr Aristide, a former Catholic priest, was Haiti's first democratically elected president, first coming to power in 1990 but serving only months before a coup removed him from office.
He returned in 1994, serving his term until 1996.
Mr Aristide was re-elected in 2000 but was forced from power in early 2004 after several months of political turmoil.
He was flown into exile on a US plane and has always accused the US of engineering his overthrow.
For the last few years he has been living in South Africa.
Mr Aristide retains a degree of political support in Haiti, though some see him as a divisive figure.
His party, Fanmi Lavalas, was barred from standing in the current election, allegedly due to technical errors in its application forms.
The delayed run-off election next Sunday is between the former First Lady Mirlande Manigat and the pop star Michel Martelly, also known as "Sweet Micky".
Both candidates have said they have no objection to Mr Aristide's return, the Associated Press reports, though Mr Martelly said it would be better to wait until after the vote.
The election campaign has been dogged by controversy.
The governing party candidate Jude Celestin was withdrawn from the race after international monitors found there had been widespread fraud in his favour in November's first round.
The US has urged Haiti's former president Jean-Bertrand Aristide to delay his return from exile until after presidential elections on 20 March.
A State Department spokesman said it was up to Haiti to decide whether the former leader should be allowed home. But he said a return before the election could be "destabilising".
A spokesman for Mr Aristide said last Friday that he would return from South Africa "in a few days" but insisted the move was not related to the vote.
Election US state department spokesman Mark Toner said that for Mr Aristide to return this week "could only be seen as a conscious choice to impact Haiti's elections".
"We would urge former President Aristide to delay his return until after the electoral process has concluded, to permit the Haitian people to cast their ballots in a peaceful atmosphere," he added.
In response, Mr Aristide's lawyer in Miami said the former president was concerned that he might lose his chance to return to Haiti once a new president was in place.
Continue reading the main story
“Start Quote
End Quote Ira Kurzban Mr Aristide's lawyerThey should leave the decision to the democratically elected government ”
The lawyer, Ira Kurzban, also questioned the US statement.
"They should leave the decision to the democratically elected government instead of seeking to dictate the terms under which a Haitian citizen may return to his country," he said. Speculation that Mr Aristide would attempt to come back to Haiti has grown since the surprise return in January of another former president, Jean-Claude "Baby Doc" Duvalier, after 25 years in exile.
Mr Aristide's lawyer collected a Haitian passport for him last month, but said the former president wanted to dedicate himself to education not politics.
Run-off vote Mr Aristide, a former Catholic priest, was Haiti's first democratically elected president, first coming to power in 1990 but serving only months before a coup removed him from office.
He returned in 1994, serving his term until 1996.
Mr Aristide was re-elected in 2000 but was forced from power in early 2004 after several months of political turmoil.
He was flown into exile on a US plane and has always accused the US of engineering his overthrow.
For the last few years he has been living in South Africa.
Mr Aristide retains a degree of political support in Haiti, though some see him as a divisive figure.
His party, Fanmi Lavalas, was barred from standing in the current election, allegedly due to technical errors in its application forms.
The delayed run-off election next Sunday is between the former First Lady Mirlande Manigat and the pop star Michel Martelly, also known as "Sweet Micky".
Both candidates have said they have no objection to Mr Aristide's return, the Associated Press reports, though Mr Martelly said it would be better to wait until after the vote.
The election campaign has been dogged by controversy.
The governing party candidate Jude Celestin was withdrawn from the race after international monitors found there had been widespread fraud in his favour in November's first round.
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