Police say they do not know who was behind the attack; the paper's exiled chief editor has blamed the government.

'South Africa shooting link'

Editor Jean Bosco Gasasira, who fled to Uganda in April after his paper was suspended, said Kigali had master-minded the assassination of Mr Rugambage who died in hospital after the shooting.

"I'm 100% sure it was the office of the national security services which shot him dead," he told US state-funded radio Voice of America.

Mr Gasasira said it was because of an article published on the Umuvugizi website relating to the attempted killing last weekend of former army chief Lt Gen Faustin Kayumba Nyamwasa in South Africa.

Rwanda has denied accusations it was behind the shooting of Lt Gen Nyamwasa.

He went into exile in South Africa earlier this year after falling out with President Paul Kagame, who he accused of corruption.

Kagame denies these charges and his government accuses Lt Gen Nyamwasa of being behind grenade attacks in Rwanda earlier this year.

In April, Kagame reshuffled the military leadership and two high-ranking officers were also suspended and put under house arrest.

Earlier in the month, Umuvugizi was suspended for six months by the press council for inciting opposition to the government.

Its website, launched in May, is not currently accessible through Rwandan internet providers; the authorities deny involvement in blocking it.

Presidential elections are due in Rwanda in August - the second such vote since the 1994 genocide.

Human rights groups have accused the Rwandan government of repressing independent media in the country, which Kigali denies.

Kagame's government argues that it must take care to control the media and politicians to avoid a repeat of the genocide, in which some 800,000 ethnic Tutsis and moderate Hutus were slaughtered.

Earlier this week, UN chief Ban Ki-moon appointed Mr Kagame to co-chair a committee of "superheroes to defeat poverty" - to push for progress in achieving the UN's Millennium Development Goals.

He has been praised for trying to modernise Rwanda's economy since coming to power at the end of the genocide.