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Derana TV in Sri Lanka says these government troops were on the frontline
Sri Lanka's key international donors have urged Tamil Tiger rebels to disarm and discuss ending hostilities in order to avoid more civilian casualties.
The US, EU, Japan and Norway said it would probably not be long before the rebels lost all territory they control.
Both sides "should recognise that further loss of life... will serve no cause", the nations said.
Sri Lanka's government says it is close to defeating the rebels. There was no immediate response from the Tigers.
Up to 250,000 civilians may be trapped by the fighting.
Separately, the army says it has found an underground bunker complex it believes was one of the hideouts of the top leader of the Tamil Tigers.
Norway, Japan, the US and the EU are described as the Tokyo Co-Chairs. They sat at the Tokyo Conference on Reconstruction and Development of Sri Lanka in 2003, which raised $4.5bn in aid pledges that were linked to progress in the peace process.
They urged the rebels to "discuss with the government of Sri Lanka the modalities for ending hostilities, including the laying down of arms, renunciation of violence, acceptance of the government of Sri Lanka's offer of amnesty; and participating as a political party in a process to achieve a just and lasting political solution".
The nations also urged both sides to "declare a temporary no-fire period to allow for evacuation of sick and wounded, and provision of aid to civilians".
The Sri Lankan government has previously ruled out any ceasefire and has vowed to crush the rebels.
The Tigers have said they will not lay down their arms until they have a "guarantee of living with freedom and dignity and sovereignty".
The Tokyo Co-Chairs said both sides "must respect international humanitarian law". They said they would help transfer internally displaced people to humanitarian camps.
The statement called on all combatants not to fire on a hospital in Tiger-held territory which has been shelled repeatedly.
The Red Cross says the hospital in Puthukkudiyiruppu town in Mullaitivu district has been hit five times in the past few days, leaving at least 12 civilians dead. One strike was on a paediatric ward, it said.
The hospital is one of the last functioning health facilities in the area.
The government says it is not responsible for the attacks and has told civilians to leave the war zone. Pro-rebel websites blame the army.
Sri Lanka's military said there was no sign of the rebel leader Velupillai Prabhakaran in the bunker found in the north-east.
Tour of the underground bunker (Sri Lanka military pictures)
The two-storey-deep bunker was found hidden in a coconut plantation in Mullaitivu district during fighting on Monday, the army said.
The ministry said the bunker had electricity generators, air conditioning and medical supplies.
There is no independent confirmation of any of the army's claims - journalists are not able to reach the front lines.
Sri Lanka's military says it has designated a safe zone for civilians in a 32 sq km buffer zone on the A-35 main road which links Paranthan and Mullaitivu.
The zone is inside a gradually shrinking rebel enclave north of Mullaitivu.
The Tigers are proscribed as a terrorist group by many nations, including the US and the EU. They started fighting in the 1970s for a separate state for Tamils in Sri Lanka's north and east.
Norway has been a broker in previous rounds of unsuccessful peace talks between the rebels and Sri Lanka's government.
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