Troops combed Sri Lanka's north-west to root out suspected rebels on Saturday after a series of deadly ambushes raised fears of a return to civil war, as the island's main donors flew to meet the Tamil Tigers for an emergency briefing.
Diplomats said donors would deliver a harsh message to the rebels after an upsurge of attacks on the military by suspected cadres culminated on Friday in an ambush on a naval bus that killed 13 sailors in the deadliest incident since a 2002 truce.
Sporadic attacks continued in the northern military-held enclave of Jaffna on Saturday evening - including a firefight in the ramparts of the town's historic fort in which the army said four Tigers with grenades and firearms were killed and two soldiers suffered minor injuries.
Soldiers checked roadsides near the site of Friday's attack in the military-held north-western district of Mannar for any more claymore fragmentation mines like the ones used on Friday. Rocket-propelled grenades were also used in the attack.
"We have taken certain actions to tighten security," said military spokesman Brigadier Prasad Samarasinghe. "We have done searches in the area where incidents have happened. In certain areas they are still going on. Search and clearance is being conducted along roads."
Friday's attack came after the first direct exchange of fire between the rebels and the navy at sea since the truce. The navy says three sailors were killed when Tiger rebels hid among a fishing fleet and attacked a patrol.
That incident in turn came after two claymore attacks earlier this month killed 14 soldiers in Jaffna, which is hemmed in by rebel lines and which the Tigers want to control.
The Liberation Tigers of Tamil Eelam (LTTE) confirmed they were involved in the naval clash but have persistently denied any involvement in a series of attacks on the military.
A delegation representing Sri Lanka's main donors - Japan, the European Union, Norway and the United States - met the Tigers' political leadership in the northern rebel stronghold of Kilinochchi to discuss a statement they issued earlier in the month calling for an end to violence.
"The meeting was about starting peace talks and stopping the violence," Tiger media co-ordinator Daya Master told Reuters. Peace talks stalled when the Tigers pulled out in 2003.
Japanese Ambassador Akio Suda, who attended the meeting, said the delegation discussed "the present situation but also explained what the co-chairs discussed in Brussels", referring to an emergency donor meeting this month.
Residents and aid workers said Mannar and Jaffna remained tense on Saturday, with troops guarding street corners as locals did last-minute Christmas shopping.
The pro-rebel Tamil Nation Labour Union Federation issued a statement asking all government departments in Jaffna to close from Monday onwards, except essential services - seen by residents as a veiled warning of impending conflict.
"Our lives are in danger again, like in the 1980s. We have had 3-1/2 years of a little peace - again it's war," said 55-year-old teacher Thevamalar Junaratnam. "We Tamils have been destined to suffer."
The Tigers threatened in November to resume their armed struggle to carve out a homeland for ethnic Tamils in the north and east unless given wide political powers in about 15 percent of the country where they run a de facto state.
New Sri Lankan President Mahinda Rajapakse, who is allied to hard-line Marxists and Buddhists who refuse any concessions for the rebels, has already ruled out a Tamil homeland and his government called on Friday on the international community to take measures to rein in the Tigers.
"The LTTE has from the very inception shown scant regard for the provisions of the cease-fire agreement," the government said in a statement overnight.
Nordic truce monitors said on Friday they had halted their unarmed patrols on the Jaffna peninsula because of the deteriorating security situation.
Many ordinary Sri Lankans fear a return to a war that killed more than 64,000 people and displaced hundreds of thousands more.