Sen John McCain made it official on Wednesday that he is seeking the 2008 Republican presidential nomination and said he plans a formal announcement in April.
The Arizona Republican, surprising few Americans, made the announcement during an interview on CBS's "Late Show with David Letterman," which was taped for broadcast late on Wednesday.
"I am announcing that I will be a candidate for President of the United States," McCain told Letterman.
McCain said he would make a formal announcement in April.
McCain has been on the campaign trail since revealing plans in November to form an exploratory committee, a key step in the campaign fund-raising process.
McCain joins former New York Mayor Rudolph Giuliani and former Massachusetts Gov Mitt Romney who are leading a large field of Republicans eyeing a 2008 White House run.
A new ABC News/Washington Post poll shows Giuliani holding a two-to-one advantage over McCain among Republicans nationally.
McCain, who turns 72 in August 2008, is a former Vietnam prisoner of war who stresses his experience in foreign policy and military affairs.
One of President George W Bush's key allies in the US Congress on Iraq, McCain called for a troop buildup for months, even after the November election when it looked like the more likely option was the beginning of a US withdrawal.
Other Republicans likely to seek the party's presidential nomination include: former Arkansas Gov Mike Huckabee, Sen Sam Brownback of Kansas, former Virginia Gov James Gilmore, former Wisconsin Gov Tommy Thompson and Reps Duncan Hunter of California and Tom Tancredo of Colorado.