MPAK, Senegal (AP) _ Loyalist forces in the West African nation of Guinea-Bissau bombarded the nearly deserted capital today as peace talks to end a 12-day rebellion were reportedly called off.

Artillery fire also could be heard reverberating across rural parts of the former Portuguese colony from across the border in Senegal, which has sent troops to fight alongside the Guinea-Bissau forces.

Government troops began shelling rebel positions in the capital of Bissau as mediation talks between rebel leader Ansumane Mane and Gambian Foreign Minister Mohamed Sedat Jobe were set to begin, Portuguese television reported.

The talks were called off because of the fighting and it was not immediately clear if they would be rescheduled. The conflict began on June 7 after rebels attempted to overthrow the government.

The Gambian mediator met with government officials Wednesday. They said they were ready to enter into talks if the rebels laid down their weapons.

But in an interview with the French newspaper Le Figaro published today, President Joao Bernardo Vieira vowed to crush the rebels, who have accused him of corruption and demanded his resignation.

Vieira said rebels were losing ground and had lost control of the military garrison in Bissau, where the rebellion began. The rebels have demanded that all peace discussion occur at the garrison.

Government soldiers _ also backed by troops from the Republic of Guinea _ have pinned down the rebels around the garrison and the international airport, bombarding what they called final pockets of resistance.

``The government operation is now focused on the airport, where the rebels are concentrated,'' Guinea-Bissau's foreign minister, Fernando Delfim da Silva, told The Associated Press in Lisbon.

A Senegalese commander said his forces were rushing heavy weapons to the capital to reinforce loyalists.

Fighting seemed to have escalated in the countryside Wednesday night and today, when the constant thud and crash of heavy artillery fire could be heard from across the border in Senegal.

More than three-quarters of Bissau's population of 300,000 has fled the city, witnesses and aid groups say.

The U.N. food agency, the World Food Program, reported some 100,000 refugees near the town of Mansoa, about 40 miles from the capital. A Catholic mission put the number at 150,000.

Refugees attempting to cross the border into Senegal were turned back by Senegalese troops who sealed the frontier on Wednesday.