Police have opened an unprecedented investigation into claims that two African heads of state with close ties to Paris have used millions of pounds of embezzled public funds to acquire lavish properties for themselves and their families in France.

The inquiry into the affairs of presidents Omar Bongo, of Gabon, and Denis Sassou N’Guesso, of Congo-Brazzaville, marks a break with the protection that was accorded to France’s African “clients” by President Chirac and other former leaders.

President Nicolas Sarkozy promised in his spring election campaign to put an end to the complicity between Paris and “la FranceAfrique”, the network that has linked French presidents with their friends in Africa since the 1960s.

Mr Bongo and Mr Sassou N’Guesso, whose countries are leading oil producers, have featured high on corruption tables issued by international watchdogs. Both were cited in recent years during French criminal inquiries into hundreds of millions of pounds of illicit payments by Elf, the former French state-owned oil group.

The prosecutors have acted on complaints from four French rights organisations over the alleged large-scale theft of international aid and national wealth by African leaders. The initial inquiry focuses on mansions and apartments that are owned by the leaders of Gabon and the Congo in western Paris.

“France can no longer remain a safe haven for the money stolen from Africans. The immunity that has been guaranteed for the past 40 years can last no longer,” said William Bourdon, the head of Sherpa, an association of international lawyers.

“This marks a first. France and other countries cannot make international commitments to fight financial crime without starting proceedings when they have real evidence of embezzlement and the siphoning of public money by the Bongo and Sassou N’Guesso families.”

The investigation is based on a recent French high court ruling that failure to justify the funding of possessions and a wealthy way of life constituted possible evidence of crime.

France has granted haven to many former Third World rulers. It has also taken part in international moves to seize the assets of some, including those of the Duvalier family, the former dictators of Haiti, and the late President Mobutu of Zaire.

France has also observed European decisions to freeze the assets of President Mugabe of Zimbabwe. However, Mr Chirac angered Britain by inviting Mr Mugabe to a France-Africa summit in 2003.

An investigating judge is likely to be appointed soon to pursue the French criminal inquiries. The judge may examine the cases of other leaders.

Odile Biyidi, president of Survival, another of the plaintiff organisations, told The Times that they had evidence of illicit acquisitions of property by other African leaders, including apartments on the exclusive Place Vendôme in Paris.

“France has too long been an accomplice in the pillaging of some of the poorest countries in the world,” she said. “The politicians closed their eyes to this. The only thing that mattered were French interests . . . They washed their hands of the rest.”

International estimates of embezzlement by Africa’s ruling families vary. In 2002 the Tax Justice Network set the figure at $30 billion (£15 billion) a year from sub-Saharan Africa.

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