Sri Lankan troops pounded Tamil Tiger positions using helicopter gunships and artillery in fierce land and sea battles in the northwest that killed at least 52 people Saturday, leading the rebels to give a strong warning of "possible retaliation."

The defence ministry said the navy and the air force together destroyed eight of the 11 boats used by Liberation Tigers of Tamil Eelam to attack a navy patrol in Mannar islet near the Palk Straits, the sea boundary dividing India and Sri Lanka [Images].

It said 30 guerrillas were killed in the fighting while 15 navy sailors were also killed. Mi-24 helicopter gunships were pressed into service to counter the rebel strike.

Hospital officials said six civilians caught up in the crossfire also died while a suspected Tiger rebel consumed cyanide pill to avoid capture.

But the LTTE denied the military figures, claiming they did not lose any of their combatants and that only two cadres were wounded.

The Tigers in a flotilla of 11 boats had attacked a naval patrol craft off the coast of Mannar. The rebel attack came after Sri Lankan military unleashed two days of retaliatory strikes after a bus bombing on Thursday in Anuradhapura, which killed 64 people.

The Tigers also shelled a police station at Pesalai in the small Mannar islet and the security forces retaliated using artillery.

In a statement sent to the Norwegian peace monitors, the LTTE gave a "strong warning to Colombo of possible retaliation following the provocative aerial bombing."

The pro-rebel Tamilnet website said at least 30 civilians were wounded in today's fighting but the defence ministry put the figure at between 15 and 20.

Meanwhile, police recovered two powerful bombs near a coastal town about 60 kilometers north of Colombo. The defence ministry said it suspected that the Tigers may have been planning a suicide mission against an unspecified target and their plans may have gone wrong.

But police chief Chandra Fernando said the Tiger frogmen had been planting limpet mines along a strategic sea lane used by the navy and where merchant shipping did not operate.

Police also reported a huge explosion, possibly at mid sea, off the coast of Negombo district which is south of Mannar.

Two men with diving equipment were arrested along the beach and they took cyanide, police said. The two were in a critical condition and admitted to hospital where one succumbed to injuries.

The escalation of violence came in spite of pressure from the international community to the warring sides to resume peace talks.

Describing the Thursday blast as an "abhorrent act of violence which marks the bloodiest attack on civilians since the signing of the cease-fire agreement in 2002," the European Union said it was "another clear violation of that agreement."

"The EU calls upon all parties to put an end to violence and to return to the negotiation table with a view to strengthening the immediate cease-fire and working towards a durable political solution of the conflict, so as to relieve the Sri Lankan people from the ordeal of 20 years of persistent conflict," it said in a statement released in Austria on Saturday.