By Patrick Nduwimana
BUJUMBURA, July 24 (Reuters) - Rebels from Burundi's last guerrilla group have quit a joint team monitoring their ceasefire with the government, further delaying a peace process meant to end more than a decade of civil war.
The most senior member of the Forces for National Liberation (FNL) attached to the team and three of his colleagues have vanished over the last three days, officials involved in the process said in a statement on Tuesday.
"The facilitation office expresses its deep regret after the disappearance of the head of FNL delegation Jean Berchimans Ndayishimiye on Saturday and that of three other members of the delegation which followed on Monday", it said.
The ceasefire monitoring team was set up after the FNL agreed a landmark peace deal with the government in September. It grouped FNL members, government officials and South African mediators and began its work in February.
"All our delegates might have left because they fear about their security", said FNL spokesman Pasteur Habimana.
He gave no other details, and many Burundians believe the rebels may have returned to the bush.
The work of the ceasefire monitoring team was repeatedly delayed by wrangling. In May, FNL delegates quit the team saying government troops had not been withdrawn from their areas. They rejoined it a month later at the urging of mediators.
The head of the government members of the team said the FNL disappearances revealed the group's bad intentions.
"It is clear the FNL wants to resume fighting, otherwise its members would not return to the bush," said Godefroid Niyombare, Burundi's deputy army chief.
Burundi's war killed more than 300,000 people and until the September peace deal, the FNL insurgency was seen as the final barrier to stability in the landlocked country of 7 million.
On Tuesday, police said they found eight mortar bombs and other ammunition hidden in a river near Bujumbura's main prison. They said they suspected the cache belonged to the FNL.