Sri Lanka imposed a state of emergency Saturday after the sniper assassination of the foreign minister, a killing that officials blamed on the Tamil Tiger (search) rebels and warned could rupture the island's fragile peace process.

Soldiers scoured the capital for suspects and helicopters and military jets patrolled over rebel-controlled territory, though the government said it had not taken steps to break the cease-fire with the Liberation Tigers of Tamileelam. The group insisted it was not responsible.

Foreign Minister Lakshman Kadirgamar (search), 73, an ethnic Tamil who led efforts to ban the Tigers as a terrorist organization but later backed peace efforts, was shot in the head and chest late Friday after finishing a swim at his home. He died after midnight.

"It is a grave setback to the peace process," an official who leads government peace efforts, Jayantha Dhanapala, told reporters. "Restarting (the peace process) will be seriously undermined."

The Tigers began fighting in 1983 for a separate homeland for ethnic Tamils, claiming discrimination by the majority Sinhalese. The civil war killed nearly 65,000 people in the country of 19 million before a Norwegian-brokered cease-fire in 2002.

Subsequent peace talks broke down, however, over rebel demands for greater autonomy in the areas under their control in eastern and northern Sri Lanka.

The rebels' political chief denied any role in the killing and criticized officials for "hastily blaming" the group.

"We also know that there are factions within the Sri Lankan armed forces operating with a hidden agenda to sabotage the cease-fire agreement," said S.P. Tamilselvan. He urged the government to thoroughly investigate the killing.

Sri Lankan officials were skeptical.

"We find it extremely difficult to accept the denial," government spokesman Nimal Siripala de Silva told reporters. "It's very, very difficult to accept."

Still, he said the government would take no action to violate the truce.

Police Inspector General Chandra Fernando (search) said six shots were fired at Kadirgamar by one or two snipers, and three bullets hit him. The assassins fired through a hole they had made in a building opposite Kadirgamar's house, in Colombo's diplomatic district.

Police said they found cheese and chocolates that the snipers ate while waiting for their target, along with a grenade launcher, apparently intended as a backup weapon.

Several people were detained for questioning, but Fernando refused to say how many. "It can be seven to 70," he said.

The state of emergency declared by President Chandrika Kumaratunga (search) empowered authorities to detain without charge anyone suspected of taking part in terrorist activities and to search and demolish buildings.

She appealed to Sri Lankans "for calm and restraint in the face of this grave and cowardly attack."

At dawn, soldiers took up positions around Colombo. They were checking all vehicles moving in and out of the city, said a military spokesman, Brig. Daya Ratnayake.

Military jets and helicopters flew over rebel-held territory, monitoring insurgent movements, and navy patrol boats guarded the coastline, some of which is Tiger-controlled, the military said.

Neighboring India called the assassination a "terrorist crime." Secretary of State Condoleezza Rice denounced it as "a vicious act of terror."

Hagrup Haukland, chief of a European truce monitoring team, called the killing a "barbaric act."

"Such brutal violence creates fear, distrust and insecurity within society, and therefore represents a serious threat to the cease-fire," Haukland said.

The slain minister, an Oxford-educated lawyer, had led an international campaign against the Tigers, who remain on terrorist lists in five countries, including the United States and Britain.

A Web site sympathetic to the guerrillas said the minister had obstructed the rebels' cause. "In short Kadirgamar was responsible for our stagnated campaign in the international scene," the pro-rebel Nitharsanam Web site said.

Rebel attacks against Sri Lankan political leaders were once common, and Kumaratunga was gravely wounded in a 1999 assassination attempt blamed on Tamil rebels.

Such high-level attacks stopped after the February 2002 cease-fire, but tensions have recently increased between the government and the rebels. There has been a surge of attacks in the volatile eastern region, occasionally spilling into Colombo.

Kadirgamar was appointed foreign minister in April 2004. He also held the position from 1994 to 2001.