SRI LANKA ? Thirteen Sri Lankan sailors were killed Friday when their convoy came under attack in the rebel-held northeastern part of the country – an incident European peace monitors fear could jeopardize Sri Lanka’s fragile cease-fire.

The attackers fired rocket-propelled grenades and triggered a land mine as about 30 sailors were traveling by bus and truck to their base in Mannar district, about 135 miles north of the capital, Colombo, said navy spokesman Cmdr. Jayantha Perera. Two sailors were also wounded, he said.

The government blamed the Tamil Tiger separatist rebels for the attack, but the rebels denied responsibility.

Violence has escalated in Sri Lanka’s northeast since rebel leader Velupillai Prabhakaran threatened to resume his struggle for an independent Tamil nation if the government fails to address grievances of the minority Tamil community.

This month alone, at least 33 government security personnel, including the sailors, have been killed and many more wounded in attacks blamed on rebels.

Envoys from Norway, Japan, the United States and the European Union – key backers of the country’s peace process – planned to meet rebel leaders today to address the escalating violence, the Sri Lankan government said in a statement.