COLOMBO, Sri Lanka - The Tamil Tiger rebels said intense fighting in Sri Lanka's war zone was killing and wounding hundreds of civilians a day and asked Wednesday for the UN to push for urgent food shipments to avert a hunger crisis.

Sri Lankan forces have cornered the once-powerful Tamil Tigers into a tiny sliver of land on the northeastern coast along with tens of thousands of ethnic-Tamil noncombatants. Many diplomats have expressed concern over the fate of the trapped civilians.

UN Secretary-General Ban Ki-moon appealed to President Mahinda Rajapaksa in a phone call Tuesday to suspend the offensive to allow aid into the war zone. Rajapaksa has brushed off calls for even a brief cease-fire, saying it would give the rebels a chance to regroup.

In a letter addressed to Ban, rebel political leader Balasingham Nadesan appealed to the international community to pressure the government to allow aid into the region and to ensure a shipment planned by Tamil expatriates makes it across the front lines.

"We draw attention to the nine deaths by starvation in the last few days and the real fear that the death toll could rise exponentially in the coming days," he wrote. A copy of the letter was e-mailed to The Associated Press by the rebels. The letter accuses the government of deliberately withholding food and medicine from the area.

Human Rights Minister Mahinda Samarasinghe said the government had delivered enough food. He accused the rebels of grabbing the supplies for themselves.

Only one shipment of food has reached the war zone in the past month, and that was 30 metric tonnes delivered by a Red Cross ship more than a week ago, said Sarasi Wijeratne, a spokeswoman for the International Committee of the Red Cross. Many aid workers said that shipment was barely enough to feed the civilians for a day.

Rebel spokesman Seevaratnam Puleedevan told The Associated Press in an interview Wednesday that the government also had violated its promise last week to stop firing heavy weapons into the war zone to safeguard civilians there.

Government troops continue to pound the area with artillery and mortar shells, conduct air strikes and attack with heavy guns from the sea throughout the night and for several hours during the day, he said.

"Most of them are falling in the civilian areas," he said. "People are living in makeshift shelters and bunkers. They are really afraid to go out because of the heavy shelling and bombardment."

Hundreds of people are being killed and wounded in the attacks each day, he said.

The military denies firing heavy weapons and says it is pushing ahead with its offensive using only small arms.

Reporters and independent observers are barred from the war zone, making the claims difficult to verify.

Speaking to reporters in New York, Ban said he asked Rajapaksa for "a humanitarian pause in the fighting" to allow aid into the conflict zone and urged the government to stop using heavy weapons.

"I repeat: Protecting civilians and respecting international humanitarian law must be priority one. The world is watching events closely, including for violations of international law," he said.

Ban also called on the Tamil Tigers -- branded a terror group by the U.S. and European Union -- to let the estimated 50,000 civilians trapped by the fighting out of the war zone and to stop forcibly recruiting fighters from their ranks.

"Above all, there is an urgent need for the two sides to bring the conflict to a peaceful and orderly end," he said.

A delegation of five British lawmakers on Wednesday urged the Sri Lankan government to "use maximum restraint" in their military offensives. Des Browne, who led the delegation on a two-day visit, asked the government to uphold it's commitment "to refrain from the use of heavy weapons."

The intense fighting since the end of January has killed about 6,500 civilians, according to UN figures compiled last month.

During the phone conversation, Rajapaksa invited Ban to visit the country and personally assess the situation, according to the president's office. UN spokesman Gordon Weiss said no decision had been made on such a visit.

Meanwhile, the humanitarian situation in the war zone had grown desperate, Puleedevan said.

Many people were surviving on one meal of porridge a day, which was being provided by the rebels or a local aid group, he said.

"All this food is drying up. Starvation and death are imminent," he said.

The rebels have been fighting since 1983 for a separate state for minority Tamils, who have suffered decades of marginalization at the hands of governments controlled by the Sinhalese majority.