The threat on Sunday came as armed rebels captured Cap-Haitien, the country's second-largest city, complicating frantic international efforts to end the crisis.
"We don't have a political objective. It will be up to the Supreme Court to assume power," said the leader Guy Philippe after 150 rebels captured the second-largest city of Cap-Haitien.
He said the role of the insurgents in a future government "depends on the new president. If he needs us, we will accept with pleasure. If not, I will return to Pestel, my birthplace and family home."
Philippe is a member of the Revolutionary National Liberation Front of Haiti and a leader of insurgents who are demanding the removal of President Jean Bertrand Aristide.
He was an officer in the disbanded Haitian army who acted as Aristide's police chief for Cap-Haitien, until he fled the country in 2000 amid charges he was plotting a coup.
Philippe warned Haiti's 5000 police the time had come to choose sides.
"They know what to do, whether they serve the Haitian people or serve tyranny. It is up to them to decide," he said.
Earlier, armed rebels who control part of Haiti's north moved into Cap-Haitien, seizing an aircraft on the way, witnesses said.
Tropical Airways manager Allen Alexandre said rebels had commandeered one of their aircraft, but the telephone line was cut before he could say more.
It was unclear what response there was from an estimated 180 police officers that Mayor Wilmar Innocent said would patrol the city during this carnival weekend. Other reports said there were only about 50.
In recent days, frightened officers have hidden behind the walled compound of the main police station, leaving the streets to Aristide loyalists who have been terrorising the population, torching homes of opponents and, on Saturday, shooting and wounding a Haitian journalist.
Rebels are demanding Aristide
step down before a ceasefire
Police had told reporters they had neither the firepower nor the numbers to repulse the guerrillas.
The rebel attack puts added pressure on politicians negotiating a US-backed international peace plan that would leave Aristide as president with diminished powers, sharing government with political rivals.
Aristide accepted the plan on Saturday, and diplomats said on Sunday they were putting pressure on an opposition coalition that is insisting there can only be peace if Aristide resigns.
The rebels also insist that Aristide steps down.
At least 61 people have now been killed since 5 February when the rebels launched their insurgency by taking the northwestern town of Gonaives.