Agathon Rwasa arrived to crowds at Bujumbura airport
Agathon Rwasa, the leader of Burundi's last active rebel group - the FNL (National Liberation Forces) - has returned home from exile in Tanzania.
His return comes four days after the FNL and government signed a ceasefire.
Correspondents say government officials were on the tarmac to welcome him and crowds lined the road to the airport.
A BBC reporter in Burundi says Mr Rwasa's return was not voluntary but followed pressure from regional leaders and an ultimatum for him to return.
The cessation of hostilities is the first step towards implementing a 2006 peace agreement.
More than 100 people have been killed and some 40,000 people displaced in renewed fighting since April.
The BBC's Prime Ndikumagenge in the capital, Bujumbura, says Mr Rwasa's return was widely welcomed.
He was accompanied by South Africa's Security Minister Charles Nqakula, who has been the chief mediator in talks between the rebel group and the government.
"This is a very important chapter in the history of this country," Mr Nqakula said.
In a speech at the airport, Mr Rwasa said, "The time has come when we have to look forward and build peace and stability for all the sons and daughters of this nation."
The government issued a statement saying the rebel leader's return would help Burundi find peace.
David Mugnier, Central African analyst for the International Crisis Group think tank, said it was a positive development which people had been "waiting for for years".
"For the first time in the history of these negotiations we will have someone accountable on the ground who is the decision maker for the rebel group," he told the BBC's Focus on Africa programme.
Our correspondent says the 2006 deal broke down after the government rejected rebel demands for power-sharing.
Ex-rebel Pierre Nkurunziza was elected president in 2005 under a deal to end years of conflict between the Tutsi army and Hutu rebels.
In more than a decade of civil war about 300,000 people were killed.