COLOMBO (AFP) - Sri Lankan troops on Tuesday seized more ground from the Tamil Tigers, as the rebels ignored a deadline to surrender and accused government forces of killing 1,000 civilians in their offensive.

Fresh fighting in the island's northeast saw the government effectively slice the last small strip of coastal jungle held by the Liberation Tigers of Tamil Eelam (LTTE) in two, the defence ministry said.

"The LTTE has not responded to the government's call to surrender, so we are keeping up our offensive to rescue the civilians," military spokesman Udaya Nanayakkara said as the midday (0630 GMT) deadline passed.

The government says its troops were poised to defeat the LTTE, a hardened guerilla group that has been fighting for an independent Tamil homeland on the ethnic Sinhalese-majority island since the 1970s.

The LTTE acknowledged they had lost even more ground, with the coastal village of Puttumatalan -- used as a key port for supplies to the rebel-held zone -- falling to government troops.

The rebels said the latest fighting had left 1,000 civilians dead and another 2,300 wounded, describing the northeast as a "bloodbath".

"The Sri Lankan armed forces are trying to weaken the resistance of the LTTE by using the Tamil civilians as human shields," the Tigers said, appealing for help from the International Committee of the Red Cross.

"The LTTE requests the ICRC provide medical supplies and evacuate by ship the 2,000 people injured and facing imminent danger," they said. "Immediate food is required as several are faced with starvation."

Sri Lankan authorities, however, denied the rebel claims. Officials in Colombo have long accused the LTTE of keeping civilians as hostage, and on Monday said nearly 50,000 men, women and children managed to escape the area.

The defence ministry also said 17 civilians who tried to escape from rebel-held territory on Monday had been killed by the guerrillas while another 373 had been wounded.

Journalists are barred from working in the north, making it impossible to verify the rival claims independently.

Government estimates show another 30,000 civilians could still be held by the Tigers but the United Nations says the number could be twice as high and warned Tuesday of the risks of an all-out final assault.

The ICRC also said it was concerned there would be a "dramatic increase" in civilian casualties.

"The situation is nothing short of catastrophic. Ongoing fighting has killed or wounded hundreds of civilians who have only minimal access to medical care," ICRC's Director of Operations Pierre Kraehenbuehl said in Geneva.

In Washington, a US official warned that time was running out for a deal that he hoped would bring lasting peace to Sri Lanka.

Michael Owen, the acting deputy assistant secretary of state for South Asia, said Sri Lanka should offer a package in which the Tigers hand in their arms, possibly to a third party, in exchange for amnesty for low-level cadres.

During the surrender, both sides would hold fire and let civilians leave, he said.

"We are running out of time," Owen told the Brookings Institution think-tank. "Really, there is literally only a couple of days to try to get this finalised."

The crisis has sparked protests in Europe and expressions of concern by UN and human rights groups.

In Paris, French police arrested 210 people Monday when a rally by Tamils turned violent as demonstrators threw bottles at security forces and smashed windscreens.

In London, thousands of Tamils blocked some of the city's busiest streets, demonstrating outside parliament and calling for an immediate ceasefire.