Rebels in Central African Republic have seized control of the country's capital Bangui, forcing President Francois Bozize to flee into neighbouring Democratic Republic of Congo.

At least six South African soldiers were killed in clashes with the rebels. A United Nations source said the force, in the country to train the army along with hundreds of regional peacekeepers, was preparing to leave.

The Seleka rebel coalition resumed hostilities this week in the mineral-rich former French colony, vowing to oust Mr Bozize, whom it accused of breaking a January peace agreement to integrate its fighters into the army.

The landlocked country, racked by rural rebellions for more than a decade, has extensive and unprotected borders and the rebel advance has added to instability in the heart of Africa.

As the loose coalition of rebels – some of them former rivals – tightened their grip on Bangui, it was unclear who would replace Mr Bozize or whether the power-sharing government of Prime Minister Nicolas Tiangaye would remain in place.

"The rebels control the town," said a presidency spokesman. "I hope there will not be any reprisals."

A government spokesman said the Seleka rebels controlled all the strategic locations in the city.

A presidential adviser said Mr Bozize, who seized power in a 2003 military coup, had crossed into Congo yesterday morning as rebel forces headed for the presidential palace.

A UN official said the Congolese government asked the UN refugee agency to help move 25 members of Mr Bozize's family out of the border town of Zongo. Congo's Information Minister said President Bozize was not among the family members who arrived in Zongo and said his arrival in the country had not been announced to Congolese authorities.

"The palace has just fallen. We have the palace," said a Seleka spokesman.

The rebels fought their way to the northern suburbs of the riverside capital late on Saturday, breaking through a line of South African soldiers during their push into the city.

About 400 South African troops are currently in the country. "I saw the bodies of six South African soldiers," a witness said. "They had all been shot. Their vehicles were also destroyed. Other South African soldiers came to recover the bodies."

A source with the UN in Bangui said South African troops were preparing to leave the country.

France, which already has some 250 soldiers stationed in the Central African Republic, has reportedly sent in another company of 150 troops to secure Bangui's international airport.

Seleka, a loose umbrella group of insurgents, fought its way to the gates of the capital late last year after accusing Mr Bozize of failing to honour an earlier peace deal to give its fighters cash and jobs in exchange for laying down their arms.

The Seleka rebels received several key ministerial portfolios under a power-sharing agreement specified by January's peace deal, and one of their leaders was named deputy prime minister in charge of national defence.

However, rebels and opposition figures accused Mr Bozize of tampering with the agreed deal to secure important ministerial posts for his loyalists.