The United States called on Liberian rebels yesterday to withdraw from the capital as fighters edged forward against President Charles Taylor?s forces and mortars continued to terrorise Monrovia?s war-weary people. A top West African official said Nigerian troops would be deployed to the battered country this week but it remained unclear whether U.S. troops would be deployed on the ground.

Residents said the rebels had advanced well beyond the key Stockton Creek bridge where fighting has been concentrated since the latest rebel assault, the third in less than two months. The bridge puts them on a road that cuts around the swamps behind central Monrovia and towards a vital junction to the main airport and Taylor?s residence.

U.S. ambassador John Blaney told reporters the Liberian government had accepted a U.S. proposal to use the Po River ? which lies 12 km (7.5 miles) from Monrovia?s outskirts ? as a new demarcation line. Blaney urged the rebel Liberians United Reconciliation and Democracy (LURD) to do the same. The LURD pushed into a suburb known as New Georgia on Sunday, residents in hiding said, adding they could hear the continuous blast of heavy weapons.

?Many innocent people are dying. Water is scarce and food is running low. Disease is out of control. If LURD has regard for the people of Liberia, it will accept this proposal?, Blaney said. ?This natural boundary (the Po River) will help verification and monitoring personnel as well as peacekeepers coming to Liberia to secure and rebuild the ceasefire?.

Aid workers said more mortars landed overnight close to a church where seven people were killed on Saturday. They said at least 20 people had been seriously wounded but it was not immediately clear if anybody was killed. Four mortar bombs had also dropped around Mechline street, in the centre of the city, wounding four.

Fighting also spread south of Monrovia, where another rebel group called Model launched fresh attacks on Saturday about 30 km (19 miles) from Liberia?s second port of Buchanan. Blaney said he was asking Model not to approach the city.

Together, the two rebel groups control some two-thirds of the country, which was founded as a haven of liberty by freed American slaves but has become a nest of anarchic fighters spreading chaos across the region. As calls for a quick deployment of foreign peacekeepers grew, the top official of West Africa?s regional bloc ECOWAS said foreign troops would arrive in Liberia this week. West African leaders have pledged to deploy some 1,300 Nigerian troops as the vanguard force of a larger mission.

The desperate humanitarian conditions in Monrovia worsen by the hour. Aid workers warn of disease and struggle to patch up the wounded as bullets zip around them. Taylor said on Saturday more than 1,000 people have died in the latest rebel assault on Monrovia. He has pledged to step down once peacekeepers arrive but has not given a precise date.

Matthew Tostevin