The fighting broke out in the Ngoma Tse-Tse region when militia forces known as Ninjas attacked soldiers guarding a rail bridge.

AFP, quoting a military source, said the Ninjas sustained heavy losses when they were forced back by government forces.

The Ninjas are loyal to former Prime Minister, Bernard Kolelas, and are in conflict with the regime of President Denis Sassou Nguesso, who seized power two years ago.

General Sassou Nguesso overthrew President Pascal Lissouba during a civil war in October 1997.

Rebel disruption

The militias retain control of parts of the centre and south of the Republic of Congo and launched an attack on the city of Brazzaville last December.

They were forced to retreat after fierce clashes with government troops.

The militias have continued to attack government targets, blowing up trains and disrupting the main rail link between Brazzaville and Pointe-Noire, the country's economic capital.

The fighting has led to a refugee crisis with many civilians fleeing into the forests surrounding Brazzaville and across the border to the Democratic Republic of Congo.

Earlier this week, ministers from the DR Congo, the Republic of Congo, and Angola signed an agreement aimed at increasing security on their mutual borders.