Rwanda opened a formal probe into 20 French officials suspected of playing a role in the 1994 genocide, in a move likely to further sour diplomatic ties with France, AFP reports.

Kigali has long accused France of complicity in the genocide of some 800,000 mostly ethnic Tutsis, at the hands of Hutu extremists, angering Paris and straining relations.

"The inquiry, for now, is focused on 20 individuals who, according to information gathered so far, are required by the prosecution authority to explain or provide clarity on allegations against them," said prosecutor general Richard Muhumuza in a statement.

This will enable prosecutors to decide "whether the concerned individuals should be formally charged or not".

Muhumuza said the relevant French authorities had been contacted and that full cooperation was expected.

The dispute centres on France's role prior to the genocide as a close ally of the Hutu nationalist regime of Juvenal Habyarimana. The shooting down of his plane over Kigali on April 6, 1994 was the event that triggered 100 days of meticulously planned slaughter.

France is accused of missing or ignoring the warning signs, and of training the soldiers and militiamen who carried out the killings.

And when the genocide was in full swing, it was further accused of using its diplomatic clout to stall effective action.

When it did finally send in troops -- in Operation Turquoise -- it was accused of only doing so to counter the advance of the Tutsi rebels of Paul Kagame, who is now president, allowing the perpetrators to escape to neighbouring Zaire which later became the Democratic Republic of Congo.