"It is our people who are dying now from bombs, shells, illness and hunger. We cannot permit any more harm to befall them," he said.
"We remain with one last choice: to remove the last weak excuse of the enemy for killing our people. We have decided to silence our guns."
Pathmanathan added that the separatist fighters' "only regrets are for the lives lost and that we could not hold out for longer".
Anura Yapa, the media minister, dismissed the ceasefire declaration, saying that "fighting is still going on in small pockets".
"We want to free this country from the terrorist LTTE," he said.
Far from the battlefield, thousands of Sri Lankans hugged soldiers, waved flags, set off firecrackers and danced to the beat of traditional drums in the streets of the capital, Colombo, celebrating the end of more than 25 years of conflict.
'Conflict not resolved'
Despite the government's apparent crushing military victory against the Tigers, however, Erik Solheim, a Norwegian minister and former negotiator in the conflict, warned on Sunday that "peace is long from being won".
|Sri Lankans in Colombo have been celebrating the end of the war [AFP]
"The Sri Lankan authorities must demonstrate generosity towards the Tamil population and grant Tamils autonomy and create a state that includes everyone," Solheim, who is Norway's international development and environment minister, said.
"The conflict is not resolved even if the battle has been won."
Norway helped broker a ceasefire in February 2002, which came to an end in October 2006 when peace negotiations broke down.
Mahinda Rajapaksa, the president, has said that after defeating the separatists, his government would begin talks towards power sharing and political reconciliation between the Tamils and majority Sinhalese government.
But many Tamils are sceptical that the victorious government will be willing to make real concessions.
Leader still at large
And with Velupillai Prabhakaran, the leader of the Tigers, still at large, the threat of renewed guerrilla warfare remains.
Narayan Swamy, the editor of Indo-Asian News Service and author of Tigers of Lanka: From Boys to Guerrillas, told Al Jazeera that it was "highly unlikely that Prabhakaran would ever surrender or show the white flag".
"Being captured alive would be the ultimate humiliation for a man who took on the Sri Lankan state with the view of breaking it up and forming an independent Tamil homeland.
"It is clear he has failed in his objective. That is bad enough," he said.
Swamy added that there remain "certain legitimate Tamil grievances".
"That's why the international community has repeatedly been telling the Sri Lankan government to get its act together," he said.
Brigadier Udaya Nanayakkara, a spokesman for Sri Lanka's military, said about 63,000 civilians who had been trapped in the war zone fled to safety in the past 72 hours.
Pathmanathan, the Tigers' spokesman, said the bodies of thousands of wounded and slain civilians lay strewn across the war zone.
|The government says "fighting is still going on in small pockets" [AFP]
Hundreds of thousands of civilians were either on the move or in camps for the displaced.
The Sri Lankan ministry of disaster management and human rights said on Sunday that it was continuing to process civilians rescued from the fighting.
Rajiva Wijesinha, a secretary at the ministry, told Al Jazeera from Colombo: "We heard that the last of them [civilians] had been saved. This was one of our great priorities in the last couple of weeks to make sure we got the civilians safely away."
Amin Awad, a representative of the UN refugee agency, said "almost all the population in the conflict zone - about 60,000 - had left".
He told Al Jazeera that the displaced were being "processed at the Omanthai crossing point. That leaves very few, if any, people in the conflict zone".
James Elder, a spokesman for Unicef, told Al Jazeera that civilians from the conflict zone were still arriving "sick and hungry" and that women and children were malnourished.
"This latest massive influx of people who have endured those extreme conditions is going to put even greater strain on those camps," he said.
"The Tamil struggle started long before the Tigers were born and will continue after the end of the Tigers"
Rajavarothiam Sampanthan, leader, Tamil National Alliance
"These camps are being created by the government, which argues they are on the basis of state security and the time needed for mines to be cleared before resettlement can occur.
"At the same time, it is urgent that the government comes out with very clear screening and separation policies and a timeline so those who are termed non-combatants are allowed freedom of movement and are allowed to resettle."
The government and the Tigers alike have been criticised for not allowing civilians to safely leave the area and for precipitating a humanitarian disaster.
More than 70,000 people have been killed in the conflict that started in 1983 and the UN says 6,000 were killed and hundreds of thousands displaced in just the last four months.
'Struggle to continue'
The Tamil Tigers once controlled nearly a fifth of the Indian ocean island nation, running a shadow state that had courts, police and a tax system along with an army, navy and even nascent air force.
But by Sunday, government troops had surrounded the remaining fighters in a 1 sq km patch of land and were seeing suicide bomb attempts and plain suicides by fighters, the military said.
However, the struggle for a homeland for ethnic Tamils who say they are marginalised by the ruling majority Sinhalese government would continue, Rajavarothiam Sampanthan, the leader of the Tamil National Alliance, told Al Jazeera.
"The Tamil struggle started long before the Tigers were born and will continue after the end of the Tigers," he said from Chennai in India.
"The Tamils have always demanded self-determination, which would mean substantial self-rule in the areas of their historical habitation."