Rwanda opposition faces intimidation-rights group

* Presidential election due in August

* Security forces investigating allegations

* Opposition leader questioned by police

(Updates with opposition leader questioned by police)

By Hereward Holland

KIGALI, Feb 10 (Reuters) - Rwanda's opposition is facing increasing threats, attacks and harassment by individuals and institutions close to the government and ruling party ahead of this year's elections, a rights group said on Wednesday.

New York-based Human Rights Watch (HRW) said the Rwandan Patriotic Front (RPF) party of President Paul Kagame, who is widely expected to win a second seven-year term in August, did not tolerate political opposition or public criticism.

Rwanda's police spokesman, Eric Kayiranga, told Reuters the security forces were investigating the harassment allegations.

HRW said three vocal opposition parties that had emerged in the run-up to this year's presidential poll had suffered serious intimidation and encountered difficulties registering.

"The Rwandan government already tightly controls political space," Georgette Gagnon, HRW's Africa director, said in a statement. "These incidents will further undermine democracy by discouraging any meaningful opposition in the elections."

Kagame, a former rebel leader whose forces ended Rwanda's 1994 genocide, has said that Victoire Ingabire -- outspoken leader of the so far unregistered United Democratic Forces (UDF) -- may be prosecuted under the nation's genocide ideology law.

The largely pro-government media have accused Ingabire of stoking ethnic division after she called for investigations into crimes committed against Hutus by the army and largely Tutsi RPF guerrillas during 1994.

The opposition leader told Reuters she was questioned on Wednesday by police who accused her of promoting genocide ideology, ethnic divisionism and of collaborating with Rwandan rebels in eastern Democratic Republic of Congo. She denies it.

Ingabire rejects charges by genocide survivor groups that she is playing the "ethnic card" in an attempt to attract votes. Last week, her aide was beaten in Kigali and later jailed on an outstanding arrest warrant for alleged genocide crimes.

HRW says the circumstances suggested the assault was well coordinated and planned. UDF said the aide was working abroad during the genocide of 800,000 Tutsis and moderate Hutus.

"On several occasions, the government has used accusations of participation in the genocide, or 'genocide ideology', as a way of targeting and discrediting its critics," HRW said.

Freedom of speech remains a delicate issue in a country where corruption of the media and the political endorsement of ethnic hatred during the early 1990s lead to the genocide, following years of dictatorship.

Frank Habineza, head of the Democratic Green Party which is largely comprised of ex-RPF, told Reuters his members had been detained without charge and beaten up. He said attempts to register his party also had been "sabotaged".

"There has been much intimidation at local levels," he said. "We think the government is failing to control the situation."

Senior government officials were in a meeting and not immediately available to comment, aides said. (Editing by Daniel Wallis and Randy Fabi)