NAIROBI, Sept 24 (Reuters) - Burundi police on Friday briefly detained a journalist investigating a grenade attack in the commercial capital Bujumbura, his radio station and an official said, after a series of explosions this week that killed at least five people.

Radio Bonesha FM said their reporter was arrested while investigating a grenade incident that was said to have killed two people on Thursday.

"Radio Bonesha FM journalist arrested on Friday morning by the police has just been released. Aimé Richard Niyonkuru is still waiting for his recorder. He spent many hours at the Special Research Office under the hot sun," the station wrote on Twitter.

Pierre Nkurikiye, spokesperson of the Interior and Public Security Ministry, said Niyonkuru had failed to identify himself as a journalist.

Burundi has suffered decades of war and ethnic and political violence.

On Monday two grenades exploded in a bus park in Bujumbura, while on Sunday a grenade attack in the administrative capital Gitega killed two, according to local media. There have been no claims of responsibility.

Congo-based rebel group Red Tabara claimed responsibility for an attack on Bujumbura airport on Saturday, saying it fired mortars as the president prepared to travel to the United Nations General Assembly in New York.

On Tuesday, Attorney General Sylvestre Nyandwi accused leaders of a suspended opposition party of being behind some recent attacks and said authorities had issued international arrest warrants for them. - George Obulutsa, Reuters