The Rwandan Government has been accused of trying to silence its opponents in the run-up to this year's elections.
The campaigning group, Human Rights Watch (HRW), says the ruling Rwandan Patriotic Front (RPF), led by President Paul Kagame, has tightened its control on the state and unfairly accused other parties of attempting to divide Rwanda.
The report also says the RPF pressurised people to join its ranks and attempted to eliminate Rwanda's second largest party, the Democratic Republican Movement (MDR).
The government rejects the criticisms.
"The RPF is not in the business of forcing people to join the party.
People in this country have joined voluntarily," Rwandan Government spokesman Joseph Bideri told Reuters news agency.
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
"I think it is very unfair to accuse the RPF of trying to have that party dissolved. The government has nothing to do with that initiative."
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 report said several individuals accused of being
"divisionist" had either fled Rwanda or "disappeared".
Mr Kagame has threatened to "wound" dissidents who oppose the government and has said the election outcome is a foregone conclusion.
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 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 also says the new constitution being drafted which will be presented to voters in a referendum later this month will perpetuate RPF control.