COLOMBO, Sri Lanka - Sri Lanka's army began observing a two-day cease-fire Monday in the war against the cornered Tamil Tiger rebels and used loudspeakers to urge thousands of trapped civilians to escape the war zone, the military said.

The government, meanwhile, dropped Norway as a mediator, accusing Oslo of failing to protect its mission there from Tamil protesters.

The two-day cease-fire took effect after President Mahinda Rajapaksa ordered the military to restrict operations to a defensive nature only for the Sri Lankan New Year. The move came amid increasing international pressure on the government to protect civilians.

UN Secretary-General Ban Ki-moon and British Foreign Secretary David Miliband welcomed the cease-fire and called on both sides to refrain from fighting.

But the lull in fighting did not set off an exodus, despite notification by loudspeaker that they should leave. Military spokesman Brig. Udaya Nanayakkara said just 18 people had left the war zone by Monday evening.

The military says the poor response may be because the rebels are not allowing the people to flee. The government and aid groups have in the past accused the rebels of holding civilians as human shields -- an allegation the Tamil Tigers have denied.

The UN says that more than 100,000 people are trapped along with the cornered guerrillas in a government-declared "no-fire" zone measuring just 20 square kilometres. It has said scores of civilians have been killed in the fighting. The rebels and rights groups have accused the military of firing into the safe zone, a charge the military denies.

Nanayakkara, meanwhile, accused the rebels of dishonoring the cease-fire by killing a soldier in sniper fire and wounding another in an artillery attack.

Government forces say they are close to crushing the 25-year separatist war after a string of battlefield victories has trapped the rebels into a small strip of land in the Indian Ocean island's north.

Sri Lankan Tamil expatriates have taken to the streets in European capitals over the past months to protest the military offensives and to demand a cease-fire.

Angered by the attacks on its embassy in Oslo, Sri Lanka's foreign ministry summoned Norwegian Ambassador Tore Hattrem on Monday and told him it was "no longer feasible for Norway to act as facilitator in the peace process," a government statement said.

The announcement was unlikely to make any difference on the ground because a 2002 Norway-brokered peace process had already collapsed and Colombo formally withdrew from a formal cease-fire last year.

The Norwegian Embassy in Colombo said Oslo police regretted they did not have enough personnel to protect the embassy.

The Tamil Tiger rebels have been fighting to create an independent homeland for ethnic minority Tamils, who have faced decades of marginalization by successive governments controlled by ethnic Sinhalese. More than 70,000 people have been killed in the violence.