Insecurity and political repression are on the rise in Rwanda in the run-up to August's presidential ballot which incumbent Paul Kagame is widely expected to win, rights group Human Rights Watch said.
The New York-based watchdog said the murder of a critical journalist, the arrest of a second opposition leader and the detention of dozens of opposition party members were attempts to muzzle dissent ahead of the poll.
"The security situation is rapidly deteriorating," Rona Peligal, Africa director at Human Rights Watch, said in a statement. "With only 45 days left before the election, the government is lashing out to silence its opponents and critics."
Authorities deny involvement in the murder of reporter Jean Leonard Rugambage, who had linked Rwandan security services to the shooting of an outspoken general in exile in South Africa.
"The government of Rwanda might have its disagreements with journalists, like other governments, but we do not kill them," government spokeswoman and foreign affairs minister Louise Mushikiwabo told Reuters by text message.
"We have requested a thorough investigation of this case and will do everything to find the culprit."
Rugambage, an editor at the banned Umuvugizi newspaper, was gunned down on June 24 outside his home in the suburbs of the capital Kigali.
Bernard Ntaganda, leader of a branch of the Social Party Imberakuri, was arrested on Thursday on charges including attempted murder and ethnic "divisionism", police said. Opposition leader Victoire Ingabire, a presidential aspirant for the United Democratic Forces party, was arrested in April.
The government rejects accusations by Rugambage's senior editor Jean-Bosco Gasasira, that it was behind the murder. International rights groups have asked for an independent probe into the killing to ensure other journalists can work safely.
Gasasira fled to Uganda when his paper, alongside another critical outlet, was suspended in April for insulting the head of state, sowing discontent in the army and causing panic.
Umuvugizi published an online article on Thursday blaming the government for the attempted murder of ex-army chief Faustin Kayumba Nyamwasa in South Africa on June 19. Rwanda's two main internet service providers have blocked the paper's website.
The government has boosted the number of army patrols around the capital at night in response to a series of deadly grenade attacks since the beginning of the year.
Regional analysts say the arrest of top military officials, the flight of a former chief of staff and a high-profile reshuffle in the army in recent months may indicate a growing schism in the central African country's leadership.
"Freedom of expression is already severely restricted in Rwanda, but the death of Rugambage is a further chilling blow to investigative journalism and, more broadly, to freedom of expression in the country," Peligal said.