COLOMBO, Sri Lanka - Sri Lanka's government urged civilians in the northern war zone to flee the fighting Friday, promising to ensure their safety amid accusations that civilians were killed after the military pounded the area with artillery shells.

Government forces have cornered the Tamil Tiger rebels in a five-kilometre-long strip along the northeast coast and appear poised to end the quarter-century civil war.

However, international pressure has grown for a cease-fire to protect tens of thousands of ethnic Tamil civilians trapped in the area. The government accuses the Liberation Tiger of Tamil Eelam rebels of holding the civilians hostage.

In a brief leaflet dropped by aircraft on the area, President Mahinda Rajapaksa appealed to the civilians to flee across the front lines, according to the government.

"Your suffering is prolonged by this action of the LTTE who are holding you as a human shield for their own safety and security," the leaflet said. "I appeal to every one of you to come over to the cleared areas."

The president promised to ensure the safety of all civilians.

Rajapaksa had earlier pledged to stop using heavy weapons in the war zone to safeguard the civilians, but reports from the densely packed war zone accused the military of continuing to launch artillery attacks and airstrikes.

A new artillery barrage began Thursday night and lasted until Friday morning, with more than 100 shells hitting the area, said a government health official in the war zone.

One shell hit the top of a coconut tree and exploded, sending shrapnel raining down on the civilians below and killing 10, the official said.

The official, who said he witnessed the attack, declined to be identified by name because he was not authorized to speak to the media.

Military spokesman Brig. Udaya Nanayakkara denied the army had fired artillery, and said the insurgents might be setting off the explosions themselves to implicate the government.

Suspected rebels also opened a new front in the war -- in cyberspace -- hacking the army's official Web site and replacing it with photos that purportedly showed civilian casualties of the war. The military, which blamed the Tamil Tigers for the cyber attack, said it planned to have the problem fixed Friday.

Concern over the fate of the estimated 50,000 civilians trapped in the war zone has grown, following a UN report that nearly 6,500 civilians were killed in the last three months.

The British and French foreign ministers called for a humanitarian truce during a rare visit Wednesday, and Japan's special mediator for the conflict, Yasushi Akashi, was in Sri Lanka on Friday to call on the government to safeguard civilians.

Rajapaksa rejected the calls for a cease-fire, and praised the war effort.

"We fearlessly stood up to a brand of terrorism that the entire world believed was invincible," he said in a May Day address Friday.

"Today various countries are calling for a cease-fire. Earlier, they asked for a cease-fire in the name of the people who were trapped in the no-fire zone. But these countries do not talk of the people who were liberated from terror," he said.

"I undertake responsibility for the people who have escaped and those who are still held by force. It is my responsibility to ensure that they will be freed with no harm," Rajapaksa said.

The Tamil Tigers have been fighting since 1983 for an independent state for minority Tamils in the north and east after decades of marginalization by governments dominated by the Sinhalese majority.

The latest military offensive has cornered them in a tiny strip of northeastern coast and appears on the verge of defeating the rebel group.

Early Friday, naval forces fired on two rebel suicide boats and a third attack craft, destroying them and killing 23 Tamil Tiger sailors, Nanayakkara said.

The government and aid groups, meanwhile, were struggling to cope with more than 120,000 civilians who fled the war zone last week, overwhelming displacement camps.

The government said Friday it had begun resettling some of those who had been displaced by earlier fighting, returning more than 400 people to their homes in the Mannar district Thursday.

Also Friday, an international press group said the military's success has been accompanied by a "brutal campaign" against dissenting media.

Paris-based Reporters Without Borders branded Sri Lanka to be the "least respectful of media freedom" among countries with democratically elected governments.

The army and certain quarters among the majority ethnic Sinhalese have harassed the private media, particularly those writing on defense-related matters, the group said in a statement to mark World Press Freedom Day, which falls on May 3.

"Media, which have been forced into exile or gagged, no longer dare to criticize or investigate military strategy," the statement said.