Liberian rebels yesterday stepped up their attack on two key bridges that would allow access to the centre of Monrovia and the seat of President Charles Taylor's power, turning down US requests for them to withdraw.

The rebels of Liberians United for Reconciliation and Democracy (Lurd) stepped up attacks on the Johnson and Old bridges yesterday afternoon, having earlier taken the key Stockton Creek Bridge, which may allow them to open up an eastern assault on the capital of the war-ravaged west African country.

The rebels turned down a ceasefire plan proposed by US ambassador John Blaney, which would have meant them pulling back to the Po River some 12 km north of Monrovia.

"We'll give up our positions to the peacekeepers only," Lurd leader Sekou Damate Conneh told AFP, referring to the proposed west African peacekeeping force that has yet to be deployed.

Blaney had earlier said that the embattled Taylor had agreed to the plan.

General Benjamin Yeaten, who is coordinating government military operations, said that Lurd had stepped up their bombardment of his position south of the two remaining key bridges, and launched two offensives during the morning, which were repulsed.

"The rebels can't take the bridges because they don't have military science, they're just bombarding, that's their only advantage," Yeaten said.

Yeaten said he would launch an offensive in the afternoon to try and establish a bridgehead in Via Town.

After Lurd troops took the northern Stockton Creek Bridge, government forces were ordered to prevent the advancing rebels from opening a new eastern front in their assault on the capital.

Yeaten and his men have taken cover in a concrete building overlooking the remaining key bridges, with rain continuing to pound the capital, as it has for days.

He said that three of his men had been killed and nine injured since the rebel assault resumed eight days ago.

It is thought that the devastating fighting has killed at least 700 civilians, with up to 200 000 people living without shelter in the capital, with little food or clean water.

To the east of the capital, rebels from the Movement for Democracy in Liberia (Model) were reportedly headed towards Liberia's second port, Buchanan.

Model military spokesperson Gal Boi Bleaju Boi said that they were respecting the ceasefire, but "if anybody attacks us from Buchanan, we can take over Buchanan to protect the civilians", many of whom fled the fighting in Monrovia.

On Friday US President George W Bush - who has so far failed to meet international appeals to lead peacekeepers into Liberia - ordered US ships to the country.

Their vaguely outlined goal will be to support a future west African peacekeeping force as it attempts to enforce a ceasefire, long since abandoned, to end nearly five years of fighting.

Meanwhile, US Deputy Defence Secretary Paul Wolfowitz reiterated yesterday that the US expeditionary force would not go into the country until there is a ceasefire and Taylor leaves power.

"They are going in when there is a ceasefire, when Charles Taylor ... has left," he told US television.

Wolfowitz dismissed suggestions that by not moving troops quickly into Liberia, the US was responsible for the continuing bloodshed.

Taylor now controls only a fifth of his west African country and is struggling to defend Monrovia.

On Saturday he reaffirmed that he would quit in line with a west African-brokered peace plan but said peacekeepers would have to arrive first, adding that they should come "in hours and not days".

The regional Economic Community of West African States (Ecowas) has pledged a 3 000-strong peacekeeping force, but has not set a date for its deployment.

Two Nigerian battalions, totalling some 1 300 men, are being scrambled as an "urgent" stopgap, with a deployment date expected to be announced today. – Sapa-AFP.