The clashes were in the district of Batticaloa on Thursday, the ministry said.

"Due to the successful retaliation, troops confirmed that 18 Tigers were killed," the ministry statement said. "Troops were also able to recover a stock of arms, ammunition and war-like materials."

It did not say if government troops suffered any casualties.

The latest clashes came as a British envoy left Sri Lanka after a three-day visit aimed at reviving the island's stalled peace bid. British member of parliament Paul Murphy is expected brief Prime Minister Tony Blair on the outcome of his visit, diplomats said.

The two sides have been trading long-range fire in northern and eastern regions in recent weeks, further damaging a truce agreed to in February 2002.

An upsurge in fighting in the past year in the island's separatist conflict has claimed more than 3,300 lives.

Meanwhile, uprooted by fighting, 130,000 people in Sri Lanka have been cut off from international assistance and are vulnerable to serious human rights abuses, a Norwegian aid group said on Thursday.

Renewed conflict in the island's north and east between the government and Tamil Tiger (LTTE) rebels has displaced about 200,000 people in all, the Norwegian Refugee Council said.

"The government as well as the LTTE have severely restricted access to conflict areas under their control, thus leaving ... displaced people and other affected populations without adequate international protection and humanitarian assistance," the aid group said in a report.