By BHARATHA MALLAWARACHI, Associated Press

Writer Sun May 21, 7:12 PM ET

COLOMBO, Sri Lanka - Suspected rebels attacked the offices of three international aid groups in Sri Lanka Sunday in what appeared to be their first assault on foreigners, the army said. Tamil separatists denied the charge.

A breakaway rebel faction said it had killed at least 10 mainstream Tamil rebel fighters and a top commander in separate attacks in the east. Four other people were also killed in spiraling violence that has threatened to push the island nation back toward civil war.

The rebels simultaneously attacked the offices of the three aid organizations in the town of Mutur in the Trincomalee District, throwing hand grenades into the buildings, said military spokesman Brig. Prasad Samarasinghe.

In an attack at the office of Nonviolent Peaceforce_ an international group that promotes nonviolent conflict resolution - a Serbian aid worker and two passers-by were wounded, said area police chief Nihal Samrakoon.

There were no injuries reported in the attacks on ZOA, a Dutch agency helping refugees, and Intersos, an Italian relief organization, Samarasinghe said.

He said he believed the Tamil Tigers were behind the attack.

The motive for the attack on the foreign groups, who have been providing assistance to refugees from the war and the 2004 tsunami, was not immediately clear.

However, government spokesman Keheliya Rambukwella said the attack appeared to be in response to mounting international pressure on the Liberation Tigers of Tamil Eelam.

In recent days, European diplomats have indicated that the EU plans to join the United States and Britain in adding the Tigers to its list of terrorist organizations.

"The timing of the attack is significant," Rambukwella said. "These are desperate moves by the LTTE and this may be a result of the pressure that has been building in the international community."

Rambukwella said this was the first deliberate attack against foreigners.

Rebel spokesman Daya Master said he was unaware of the attacks, but "the LTTE would never attack NGOs and foreigners."

Aid workers said it was unclear why they had been targeted or who was behind the attacks.

"At the moment, we have no idea why," said Nonviolent Peaceforce project director Marcel Smits. "It is something we have to look into to see what could possible be behind this. It seems like it was coordinated," he said.

Also Sunday, 15 people were reported killed in ongoing violence that has shaken a fragile 2002 cease-fire between the government and rebels, halted peace talks and left at least 275 people dead since April, according to international truce monitors.

The rebels have fought the government since 1983, demanding a separate Tamil homeland. More than 65,000 people were killed before the cease-fire halted 19 years of open warfare.

A breakaway Tamil faction said their forces had attacked a mainstream Tamil Tiger camp near Trincomalee, killing at least 10 rebel soldiers.

T. Thuyavan, a spokesman for the breakaway Karuna faction said their forces attacked the Tiger camp with mortars and RPGs before overrunning the site and killing the Tamil fighters.

Karuna forces also killed a top Tamil Tiger rebel commander near the eastern city of Batticaloa, Thuyavan said.

Tamilnet, a pro-rebel Web site confirmed that the leader, named Ramanan, had been killed, but said he was "assassinated" by army snipers.

The rebel movement split in 2004 when an eastern-based military commander named Karuna broke away with 6,000 fighters.

In the eastern town of Mavadivembu, a 12-year-old boy was killed by suspected rebels late Saturday as he sat at his home with his grandmother, an army statement said.

The army said he was killed after spurning attempts by the Tigers to recruit him. The rebels have been criticized for recruiting child soldiers.