Pierre Pean has previously written books about French politics
A prominent French writer, Pierre Pean, is on trial in Paris accused of inciting racial hatred in a book on the Rwandan genocide.
Mr Pean wrote that the Tutsis had a culture of lies and deceit, and this had somehow spread to the Hutus.
He said it made investigating Rwanda "an almost impossible task". Some 800,000 Rwandan Tutsis and moderate Hutus were slaughtered in 1994.
A French rights group, SOS Racisme, filed the lawsuit against Mr Pean.
The case against him is backed by the public prosecutor. It centres on four pages in Mr Pean's book Noires Fureurs, Blancs Menteurs (Black furies, white liars), published in 2005.
In remarks broadcast on French radio on Wednesday, Mr Pean said he "wrote a book on lies, misinformation, which were, I believe, conducted through extremely elaborate methods, whereby a dictatorial regime wanted people to believe in lies".
An investigative journalist, Mr Pean wrote a bestseller about former French President Francois Mitterrand, among other works.
Historians, other experts and politicians, including former foreign minister Hubert Vedrine, are due to testify this week. The verdict is expected at a later date.
Hutu militias carried out mass slaughter in just 100 days
SOS Racisme president Dominique Sopo said that "when you are aware what cliches can trigger in terms of killings, racism and confrontation, especially in that country, it seems to me that this particular issue greatly disturbs those who went through such drama and who prefer not to go through it again".
France has consistently denied any responsibility for the genocide, rejecting claims by the Rwandan government that French officials played an active role in it.
An independent Rwandan commission said France had been aware of preparations for the genocide and helped train the ethnic Hutu militia.
The two countries have had a frosty relationship since 2006, when a French judge implicated Rwandan President Paul Kagame in the downing in 1994 of then-President Juvenal Habyarimana's plane - an event widely seen as triggering the killings.
President Kagame has always denied the charge.