(Adds new fighting)

COLOMBO, Feb 20 (Reuters) - Sri Lankan troops launched a new offensive against a Tamil Tiger rebel-held area in the north on Wednesday, the Defence Ministry said, and a top United Nations official began a week-long tour of the island.

Fighting between the military and the Liberation Tigers of Tamil Eelam (LTTE) has intensified since the government scrapped a six-year-old ceasefire pact last month. The government said the rebels had used the truce to re-arm.

"Troops continued to surge into LTTE territory towards Adampan junction in a fresh offensive launched at 6 a.m," the Ministry of Defence said in a statement on its Web site.

The ministry also said at least 30 rebels and three Sri Lankan soldiers had been killed on Tuesday in a series of engagements along the frontline separating government and rebel forces in the north and northwest.

The military said 13 Tamil Tiger rebels were killed from confrontations in the northwestern district of Mannar on Wednesday while two soldiers were killed. It said it believes over 40 Tamil Tiger rebels were killed or wounded in the confrontation on Monday in the same area.

Suspected rebels also killed three soldiers on Wednesday during an ambush in the far south.

The Tigers were not available for comment and analysts say both sides tend to inflate enemy casualty figures in the absence of independent accounts of the fighting.

The latest fighting came as U.N. Assistant Secretary-General for Political Affairs Angela Kane arrived in the Indian Ocean island nation to kick off a week-long mission described by the world body as a regular follow-up visit.

The ambush in the far southern district of Monaragala occurred near Yala national park, which is popular with foreign tourists. Attacks in the south are rare.

"LTTE terrorists fired at an army checkpoint in Galge and killed all three soldiers on duty," military spokesman Brigadier Udaya Nanayakkara said.

A search operation was under way for the attackers.

Buoyed by battlefield victories in the east, where it has captured swathes of rebel-held terrain, the government is now seeking to overrun the separatist Tigers' northern stronghold in the latest chapter of a 25-year civil war.

But the Tigers continue to mount suicide attacks and roadside bombings.

The International Committee of the Red Cross says it is concerned about the growing number of civilian casualties in Sri Lanka, where the civil war has killed more than 70,000 people since 1983.

The ICRC said 180 civilians were reported killed and almost 270 wounded so far this year in bombings on buses, train stations and in the streets. The Sri Lanka government has blamed most of the attacks on the rebels. (Reporting by Ranga Sirilal; Editing by Elizabeth Piper)

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