Former New York Mayor Rudolph Giuliani has taken a key step towards running in the 2008 US presidential election.
Rudolph Giuliani is considered a moderate Republican
He is setting up an "exploratory committee", the first stage in any presidential bid, his representatives have said.
Mr Giuliani was widely praised for his response to the 9/11 attacks on the World Trade Center in New York in 2001.
He is known as a moderate Republican who supports gun control, same-sex civil unions and abortion rights.
"Mayor Giuliani has not made a decision yet," his spokeswoman said in a statement on Monday.
"With the filing of this document, we have taken the necessary legal steps, so an organisation can be put in place and money can be raised to explore a possible presidential run in 2008."
Under US law, setting up such a committee allows Mr Giuliani to travel the country to gauge support for a candidacy without formally declaring himself as a candidate.
Being mayor, even in a city as big and important as New York, is not commonly regarded as normal preparation for a presidential campaign, says the BBC's Jeremy Cooke in New York.
But he adds that in the chaos which followed the devastating attacks on the World Trade Center, Mr Giuliani emerged as a defiant and unifying leader, earning him the honorary, wholly unofficial title of "America's mayor".
Since then, Mr Giuliani has remained in the public eye and has remained popular with the American people, particularly Republicans.
His relatively moderate views may make it difficult for him to persuade mainstream Republicans that he should be their presidential candidate.
His support for same-sex civil unions and embryonic stem cell research would put him to the left of most of his party members.
One potential rival for the Republican Party nomination is Arizona Senator John McCain, who said on Sunday that he planned to set up his own exploratory committee.