The Rwandan Government has denied accusations that the ruling Rwandan Patriotic Front (RPF), led by President Paul Kagame, has clamped down on the opposition in the run up to this summer's election.
Presidential envoy Patrick Mazimpaka told the BBC that the report published by the New York-based Human Rights Watch (HRW) "misrepresents the facts".
The report accuses the RPF of attempting to eliminate Rwanda's second largest party, the Democratic Republican Movement (MDR).
"The RPF alone cannot be responsible for the decision in parliament to investigate the MDR party... Parliament will do things its not told to do by the government," Mr Mazimpaka said.
With the formation of new parties impossible and the one significant old party dissolved, the RPF will have assured the
electoral victory it so badly wants
"The MDR cannot claim to be the main party... It came into being as a Hutu party, a party that advocated dividing the country into two parts. A party that is exclusively for one ethnic group."
"That is an ideology which is no longer acceptable... to Rwandans after it lead them to genocide in 1994," he continued.
He said most of the people who the report says have been locked up are actually in Uganda.
The HRW investigation also said the RPF had last year banned the creation of other parties.
"With the formation of new parties impossible and the one
significant old party dissolved, the RPF will have assured the
electoral victory it so badly wants," Alison des Forges of Human
Rights Watch said.
The RPF came to power following Rwanda's 1994 genocide, in
which extremists from the Hutu majority organised the massacre
of an estimated 800,000 minority Tutsis and moderate Hutus.
The party says it has rejected the ethnic divisions of the past but has been accused of using the need for unity to justify increasing its grip on power.
This year's election, due in July, is the first since the genocide and marks the end of a transitional period, originally mapped out for five years but later extended to nine.
HRW has also said the new constitution being drafted which will be presented to voters in a referendum later this month will perpetuate RPF control.