By Patrick Nduwimana

BUJUMBURA (Reuters) - Burundi's army said on Thursday it had killed 50 fighters from the country's last active guerrilla group in renewed clashes outside the capital Bujumbura.

The attack comes barely a day after leaders of the Forces for National Liberation (FNL), an ethnic Hutu group, said they would return to the tiny coffee-growing country from exile to implement a long awaited peace deal.

"The Forces for National Liberation ambushed our troops on patrol, the army then entered into heavy battle with the insurgents ... two soldiers were also killed," army spokesman Colonel Adolphe Manirakiza said.

He said four soldiers were wounded, 31 rebels captured and several weapons seized.

The rebel group blamed the army for the fighting.

"It is really regrettable, at the time we were ready to come back to Burundi to continue talks with the government, the army decided to intensify attacks against our positions," spokesman Pasteur Habimana said from Dar es Salaam.