Sri Lankan officials and Tamil Tiger rebels have met face-to-face for the first time in three years to try to shore up a threadbare four-year truce.
The two sides disagree over how the truce has been implemented
Two days of talks are being held in the Swiss city of Geneva. Recent violence has raised fears of a return to war.
Norwegian peace envoy Erik Solheim, who brokered the talks, warned against expecting too much from the meeting.
The ceasefire agreement in February 2002 preceded several rounds of peace talks, which stalled in April 2003.
The latest talks began with the government's chief negotiator, Nimal Siripala de Silva, and the Tamil Tigers' Anton Balasingham shaking hands at a secluded chateau just outside Geneva.
"Strengthening of the implementation of the ceasefire itself is an extremely important agenda," Mr Solheim told reporters.
But he stressed that expectations from the talks should be "realistic". "Confidence can only increase, but they have started at a very low level."
Ahead of the meeting, the Tamil Tigers said six men in military uniforms had attacked one of their posts in eastern Batticaloa district on Wednesday, killing one of their members.
"The attack has raised serious doubts in the minds of Tamil people about the sincerity of the government in taking part in direct talks," the rebels said on their website.
The army denied involvement, calling the allegations "baseless and malicious".
In the northern town of Jaffna, Hindu, Christian and Muslim clergy led prayers for peace at a public hall to coincide with the talks.
Sri Lankan civilians have been caught up in the violence
The BBC's Imogen Foulkes in Geneva says diplomats are playing down hopes the talks can achieve anything more than restoring some stability in Sri Lanka.
"If they fail, I really do believe there will be war," an unnamed European diplomat is quoted as saying by Reuters.
At least 120 people - including about 80 soldiers and sailors and many civilians - have died in the upsurge of violence, which began soon after Mahinda Rajapakse assumed the presidency in November but has abated since the deal to hold talks was reached last month.
The attacks on the military have been blamed on the rebels, who deny involvement.
Tamil Tiger supporters say more than 40 Tamils have been killed by the security forces in a series of attacks since the start of December. Others blame some of those deaths on the rebels or other armed groups.
The talks are being held in Geneva after the Tigers refused to negotiate in any Asian country.
More than 60,000 people died during two decades of conflict in Sri Lanka.
The Tamil Tigers want autonomy for minority Tamils in the north and east. President Rajapakse has said the solution to the conflict lies in a unitary state.