The diplomats from the quartet known as "Co-Chairs" left for the rebel-held northern town of Kilinochchi on Saturday, 330km (206 miles) north of Colombo to meet the rebel political wing leader S P Thamilselvan, officials said.

The visit follows a meeting Ratnasiri Wickremanayake, the prime minister, held with representatives of the Co-Chairs - the US, European Union, Japan and Norway - after Friday's suspected Tamil attack on a naval road convoy.

At least 15 sailors were killed and an equal number wounded in the attack while three more people were killed in violence linked to the conflict, officials said.

The government said: "The prime minister impressed upon the need for the international community to take specific measures to ensure that Tamil Tigers desist from further escalating violence and return to the negotiating table."

It said the Liberation Tigers of Tamil Eelam (LTTE) had shown scant regard for a truce Norway mediated and put in place since February 2002.

LTTE statement

Friday's attack against the navy was the worst against government forces since the truce.

There was no immediate word from the guerrillas to charges they staged the attack in the northwestern coastal region of Mannar, but the official Tiger website said the military demonstrated a knee-jerk reaction.

The LTTE said in a statement: "The Sri Lankan army has been taking knee-jerk aggressive military actions in dealing with recent incidents in Jaffna and Mannar.

"People of both areas are expressing fear that the Sri Lankan army continues to be a threatening presence."

Security surge

Military officials said security had been stepped up across the island after the spike in rebel attacks that left at least 60 people dead this month alone.

It was also the bloodiest month for the military which has lost 18 sailors, 19 soldiers and two constables during the same period.

"This is a cowardly attack. It is disgusting. There are elements who do not want peace in this country"

Hagrup Haukland,
Norwegian-led truce monitors head

Hagrup Haukland, the head of the Norwegian-led truce monitors, said the situation in the island-nation was alarming and that the ceasefire was in jeopardy.

"I commend the security forces for acting with restraint," Haukland said on Friday night. "On the other hand, the other party (the LTTE) and the Tamil people accuse the security forces of being too tough against them.

"This is a cowardly attack. It is disgusting. There are elements who do not want peace in this country."

He declined to name the elements, but said the target of recent attacks had been security forces.

Funding

The upsurge in violence came as Thamilselvan warned that there could be more clashes with the navy unless truce monitors made arrangements for the LTTE to have safe passage using sea lanes.

The surge in clashes came despite a warning by the Co-Chairs to Tigers to end the latest cycle of violence.

The quartet has promised billions of dollars to rebuild the country's war-shattered economy if the two sides show progress in ending three decades of bloodshed that have claimed more than 60,000 lives.