"We are continuing the investigation and questioning the two suspects," notably on whether any link exists between the blasts and the August presidential election, he said.

'Political harassment'

Rwanda is due to hold a presidential vote in August in which Paul Kagame, the country's president, is widely expected to seek and secure re-election.

Kagame, who heads a Tutsi-led government, has been in power since the end of the genocide in 1994.

Earlier this month, the New York-based Human Rights Watch (HRW) condemned the harassment of political opposition figures in Rwanda, saying they faced increasing "threats, attacks and harassment" ahead of the poll.

The group cited an incident in which Joseph Ntawangundi - a member of the FDU-Inkingi, a new opposition party critical of government policies - was attacked in front of a local government office.

"The attack appeared to have been well co-ordinated, suggesting it had been planned in advance," HRW said.

Ntawangundi has since been jailed after being sentenced in absentia in 2007 to 19 years by a court set up to try the perpetrators of the genocide.

Sarkozy visit

The attacks come just days before a visit by Nicolas Sarkozy, the French president, to Rwanda, aimed to cement newly renewed diplomatic ties between Paris and Kigali after years of mutual recriminations over the 1994 genocide.

Sarkozy's trip next week will be the first by a French president since the massacre by extremist Hutus of around 800,000 people in Rwanda, mostly Tutsis and moderate Hutus. A new French ambassador to Kigali was accredited in January.

The two countries announced in November the resumption of relations severed in 2006 after a French judge issued warrants against President Kagame's top aides on suspicion of being behind the death of a Rwandan ex-president.

For its part, Kigali alleged French forces had trained extremist Hutu militia which carried out the killings, a charge Paris has repeatedly denied.