Rwandan President Paul Kagame said Monday he expects "justice to be done" after his predecessor's widow was arrested over the 1994 genocide -- and criticised French and international justice systems.

Agathe Habyarimana, 67, is the widow of Juvenal Habyarimana, whose assassination was seen as the signal for Hutu militias to launch the massacre of minority Tutsis, in which an estimated 800,000 people died.

She was arrested this month at her home outside Paris after an international warrant was issued on October 19 by Rwanda's chief prosecutor.

Kagame was asked about the case as Rwanda was formally welcomed to the Commonwealth in London Monday on Commonwealth Day. He was also attending a service at Westminster Abbey with Queen Elizabeth II.

"Whichever ever case we go, we expect justice to be done. That's the aim of our country, whether we try such cases or such cases are tried elsewhere, so be it," Kagame said.

He criticised France for not acting sooner but hoped the country might now "want to try the case to its conclusion".

"This person who has committed these crimes has been sitting in France that is supposed to be a developed justice system (in) which you have expected that you would see her trial," he said.

"It hasn't happened for the last 16 years. She has been arrested in France, well and good, maybe it's never too late in this case."

He also said that international courts had "been held for the last 14 years, tried only about 50 cases, spent billions of dollars and we see more people all over the place who should be tried who are not tried."

Habyarimana was arrested a week after French President Nicolas Sarkozy visited Kigali. She is accused of being a member of the Hutu inner circle that planned the mass killings and strongly denies the charge.