By Paul-Marin Ngoupana

BANGUI (Reuters) - The president of Central African Republic dismissed the head of the armed forces on Tuesday after days of fighting with gunmen loyal to ousted leader Francois Bozize that left 100 people dead, a government spokesman said.

Calm returned on Tuesday after fierce clashes between government forces and pro-Bozize fighters in Bossangoa, Bozize's home region, about 300 km (185 miles) north of the capital Bangui.

The fighting was the latest sign of instability since the Seleka rebel group seized power in March in the landlocked former French colony, plunging the nation of 4.5 million people into chaos and a deepening humanitarian crisis.

President Michel Djotodia, the former leader of Seleka, named General Ferdinand Bombayake as the new head of the armed forces in a series of changes to military top brass, state radio announced.

Bombayake was the head of security for ex-president Ange Felix Patasse, who was toppled in a 2003 coup by Bozize.

"The change at the head of the army today is linked to the current situation in the country's north and the president's desire to bring some corrections in the security sphere," his spokesman Guy Simplice Kodegue said.

Kodegue said an estimated 100 people had been killed in fighting in Bossangoa and nearby Bouca with Bozize's supporters between Saturday and Monday.

Some 30 houses had been burned and two bridges demolished, cutting off the region from the capital, Kodegue added.

The fighting came after a U.N. warning that Central African Republic was on the brink of collapse. Muslim Seleka fighters are targeting the Christian populations of the country's north.

Bozize, who fled first to Cameroon and then to France, told French media in Paris last month that he still had ambitions of returning to power.

The rebellion in CAR - one of the poorest places on earth - has triggered a humanitarian crisis after many aid groups and U.N. agencies pulled out, leaving people to fend for themselves.

(Reporting by Daniel Flynn; editing by Mike Collett-White)