The comments from S Paliakkara came as dignitories attended the funeral of assassinated Foreign Minister Lakshman Kadirgamar, a killing the government blames on the Tigers.
Military forces fanned out across the capital, Colombo, as foreign officials mingled with saffron-robed Buddhist monks to pay their respects to Kadirgamar amid fears his death could scuttle a three-year ceasefire.
The Tigers have denied government claims they were behind the assassination of Kadirgamar - one of their most vociferous critics - and urged the military to look within its own ranks for the perpetrator.
Paliakkara said he had briefed foreign ambassadors in Colombo and told them in a meeting on Sunday that the assassination bore the hallmark of the Tigers.
"This has gone too far. The international community must understand this is a serious setback to the peace process," he said on Monday.
Paliakkara said he had urged the international community to take "strong anti-terrorist measures" against the group. He did not elaborate.
But another official, speaking on the condition of anonymity because of the sensitive nature of the requests Sri Lanka has made to other countries, said the island nation wants foreign governments to keep a closer eye on groups and individuals who support the rebels' cause, to restrict their travel and to stop their ability to raise money.
"This has gone too far"
The Tigers began fighting in 1983 for a separate homeland for minority ethnic Tamils, claiming discrimination by the majority Sinhalese. The war killed nearly 65,000 people in this country of 19 million before a 2002 ceasefire.
But subsequent peace talks broke down over rebel demands for greater autonomy in the areas they control in the north and east. Monday was declared a day of mourning, and schools, cinemas and shops were ordered closed.
White flags fluttered across the capital to show respect for Kadirgamar, shot by snipers on Friday night as he stepped from his pool at his Colombo home.
"The evil hand of terrorism, which threatens the very fabric of civilised society, has taken away yet another champion of peace," Prime Minister Mahinda Rajapakse said in a speech before the cremation.
The Tamil Tigers deny carrying
out the assasination
President Chandrika Kumaratunga, wounded in a 1999 rebel bomb attack, ignored security concerns and attended the funeral. A white carriage with a golden dome bore Kadirgamar's flag-draped coffin to Colombo's Independence Square, where most Sri Lankan dignitaries are cremated.
Brass bands accompanied the coffin to the square, where it was placed on a pyre of logs covered by a white, temple-shaped tent.
After speeches and honors, Kadirgamar's son Ragi lit the pyre and the late foreign minister was cremated according to Buddhist tradition.
A state of emergency was ordered within hours of Kadirgamar's slaying on Friday. More than 1000 security personnel, including dozens of anti-terrorist commandos, kept watch during the funeral.
Sri Lankan soldiers on guard in
the capital Colombo
Black and white banners hung around the city blamed the Tigers for the assassination.
"Let us bury the (Tigers) and end this carnival of killing," said one banner put up by the National Movement Against Terrorism and by a group of Buddhist monks.
Blaming the Tigers
"We honour Minister Kadirgamar, brutally gunned down by the (Tigers)," said another. "There is no point in talks - we have to go back to war to save the country. This cannot be done through dialogue," said Gamini Peiris, a 37-year-old Sinahlese Sri Lankan.
Sri Lanka's Sinhalese majority, mostly Buddhists, number about 14 million people. The 3.2 million Tamils, mainly Hindus, are concentrated in the country's north and east and in its central tea-growing hill country.
Kumaratunga on Sunday blasted the rebels as terrorists and said there was evidence linking them to the assassination. But she also vowed not to give up on the peace process, which most here believe is the best hope of ending two decades of bloodshed.
"We must prevail to ensure that Lakshman Kadirgamar's sacrifice has not been in vain," the president said in a nationwide television broadcast.
Norwegian Foreign Affairs Minister Jan Peterson, one of the architects of Sri Lanka's now-stalled peace process, also attended the ceremony and was set to meet with Kumaratunga later on Monday to discuss the peace process.