Hundreds of people continue to flee the Republic of Congo's western Pool region, where fighting has been raging in recent days between the army and opposition militia gunmen known as Ninjas.

Relief workers say the refugees are heading to the region's main city, Kinkala, and to Congo's capital, Brazzaville. Some of those arriving in Brazzaville from the Pool region are giving accounts of government forces attacking suspected Ninja positions with helicopter gunships.

The latest hostilities broke out last week after government officials said Ninjas attacked a passenger train traveling between the port city of Pointe Noire and Brazzaville. Officials say two people were killed and a number of others wounded in the assault.

Congo has experienced three civil wars over the past decade that killed, according to the official tally, at least 15,000 people. The conflicts pitted rival factions that were divided along political and ethnic lines. The Ninja militia took up arms against another group known as the Cobras, who supported President Denis Sassou-Nguesso. The Ninjas backed former Prime Minister Bernard Kolelas - who, along with President Pascal Lissouba - was ousted by forces loyal to Mr. Sassou-Nguesso in 1997.

The fighting that broke out last week is the worst to occur in Congo since peace returned in 1999. The skirmishes are raising fear among many that the country might slide back into a full-fledged conflict.

President Sassou-Nguesso was reelected by a landslide last month. Many Congolese credit him for consolidating peace in the country following the signing of the 1999 cease-fire.

A cease-fire agreement called for the reintegration of militias in to the armed forces. The Ninjas, however, complain that reintegration has not occurred. The head of the Ninjas - who refers to himself as Ntula - refused to attend a dialogue between the government and the opposition last year, saying his demand for a high-ranking military post and other concessions had not been granted.

Pascal Lissouba and Bernard Kolelas remain in exile. Both have been convicted in absentia on charges related to the conflicts of the past decade. Neither man was allowed to run in the March presidential elections.

In his strongest statement since the start of the hostilities, President Sassou-Nguesso late Sunday warned he would not allow any group to threaten peace and security in Congo. Government officials have vowed they will take all measures necessary to restore order in the Pool region.