PUTHUKUDIYIRUPPU, Sri Lanka (Reuters) - After 25 years of war, Sri Lanka army Brigadier Shavendra Silva is measuring the last of the fighting in days.

Standing not far from where he expects a final showdown with Tamil Tiger separatists in the Indian Ocean island's northeast, the 58th Division commander ordered in his armored units as Tiger mortar bombs exploded on the nearby frontline.

Three T-55 tanks and an armored personnel carrier with a 30 mm cannon raced down the A-35 road, throwing up clouds of fine red dust, the thump of their 30 mm cannon heard within a minute.

Just a few hours earlier, the Liberation Tigers of Tamil Eelam's (LTTE) peace secretariat had issued a letter addressed to the United Nations and others saying the separatist guerrilla group would accept a truce but not surrender.

We have a job to do. We are not bothered about any truce at the moment, Silva told Reuters Monday on a visit to a frontline usually closed to outside observers.

Sri Lanka's military has cornered the LTTE in less than 60 sq km (23 sq miles) of palm-dotted coastal scrubland and expects to end one of Asia's longest-running wars shortly.

How long it will take is not in weeks. I am talking in days, Silva told Reuters earlier at his headquarters in Kilinochchi in the three-storey former LTTE Peace Secretariat where the Tigers once hosted diplomats and journalists.

Silva's troops seized the northern half of Kilinochchi, which the Tigers had proclaimed as the capital of the separate state they wanted to create for Sri Lanka's minority Tamils, on Jan 2.

Since then they have moved swiftly east more than 30 km along the A-35 road.

Much of the road itself shows little sign of war save the soldiers, but there is plenty of destruction around it. Houses, shops and fences lie in disarray, felled by a wall of water loosed when the LTTE blew up the Kalmadakulam dam.

The water was nine feet high. The brigade commander was on top of a tree, Silva said near a bridge that had also been blown up by the LTTE during its retreat.

Further along is a refugee reception center, where more than 25,000 people fleeing fighting were screened before being moved to camps outside the war zone.

Witnesses who have escaped said the LTTE forced civilians to stay as conscripts or human shields, shooting those who tried to escape and firing artillery from areas thick with people.

The Tigers have in turn accused the government of indiscriminately shelling civilians, which the military denies and says is part of an old Tiger strategy to manufacture a crisis to create international pressure for a ceasefire.

They are firing a lot from the no-fire zone but we can't help it. We don't fire into the no-fire zone. We fire immediately to the front of our line, Silva said.

The civilian presence has forced the military to slow down its advance and take more of its own casualties, commanders say.

If it weren't for the civilians, this would be a one-day job, Major-General Jagath Jayasuriya, overall commander for the war zone, told Reuters from his headquarters in Vavuniya, 75 km (45 miles) south of Kilinochchi.

Aid agencies say there are 200,000 people stuck in the war zone, while the military puts the number at no more than 70,000.

Nearly all of them are in the current no-fire zone, a narrow 12-km strip of mostly coconut groves bounded by the ocean on one side and a lagoon on the other.

Troops are to the north and south, and Silva's soldiers were 6 km (4 miles) from the lagoon's western shore Monday.

That is where Silva expects the final showdown.

We will have to see how the LTTE will react at the end of that area, he said.