PORT-AU-PRINCE (Reuters) - Around 3,000 followers of Haiti's ousted former President Jean-Bertrand Aristide marched in support of his return from exile on Friday, and protest leaders threatened to disrupt an upcoming presidential run-off vote if his homecoming is blocked.

The noisy march by pro-Aristide protesters converged on the earthquake-damaged presidential palace in the crowded capital Port-au-Prince, but ended peacefully under the eyes of Haitian riot police and United Nations peacekeepers.

The demonstrators carried banners with slogans like "Titide (Aristide) we are waiting for you" and chanted "Aristide or Death." Some waved posters of the firebrand populist former president, who was ousted in a 2004 revolt and has lived in exile in South Africa. He has a passionate following in his Caribbean homeland, the Western Hemisphere's poorest state.

Aristide's announcement last month that he plans to come home has generated widespread anticipation in Haiti, which is struggling to recover from a crippling 2010 earthquake and held a chaotic first round of presidential and legislative elections in November.

Haiti's government has issued a diplomatic passport to the former leader, who is expected back in the coming weeks, although exactly when is still uncertain.

The United States and other western aid donors, who have pledged billions of dollars for Haiti's post-quake rebuilding, fear that the return of such a polarizing figure as Aristide would be disruptive, especially if it occurs before the decisive presidential run-off on March 20.

The presidential run-off pits former first lady Mirlande Manigat against musician Michel "Sweet Mickey" Martelly.

"The U.S. has no right to decide whether President Aristide should come back or not," said Rene Civil, one of the protest organizers and a local leader of Aristide's Fanmi Lavalas party, the country's biggest, which was excluded from the current elections over previous registration problems.

'A WARM-UP SESSION'

Civil warned that if outgoing President Rene Preval and his foreign donor partners do not facilitate Aristide's return, Aristide supporters would mobilize in protest and this could block the presidential run-off election.

"Today was just a warm-up session," he told Reuters.

"Without a return (of Aristide), there won't be a second round," the pro-Aristide protesters chorused in Creole.

They also called for the cancellation of the elections, which have been plagued by fraud allegations and protests.

"They pushed Lavalas to one side, and we're the most popular party in the country. There can't be a real election, its a 'selection' without Lavalas," said one of the demonstrators, Jonnie Narcisse.

Aristide became Haiti's first freely elected president in 1991 but was deposed by a coup after only seven months.

Re-elected in 2000, his second term was soured by economic instability and gang and drug-trafficking violence. He was ousted again in a 2004 rebellion that included former soldiers. Aristide claimed it was orchestrated by the United States.

Haiti's fight to recover from the devastating earthquake a year ago has been complicated by a cholera epidemic which has killed more than 4,500 people since mid-October.