Tamil Tiger rebels say they will not meet the Sri Lankan government for more peace talks which were due to be held in Switzerland next week.
The Tigers say they are being pushed towards war
The Tigers said their decision came after a recent escalation in violence in the Tamil-majority areas.
They said they would not set a new date for talks until "normality returns".
Dozens of people have been killed in a surge of violence since 8 April. The Tamil Tigers have denied being behind attacks on the military.
Rebel political leader SP Thamilselvan said he had conveyed the decision to Norwegian peace envoy Jon Hanssen-Bauer following a meeting in the rebel-held northern town of Kilinochchi.
Dozens of people have been killed in the last week
"We are not in a position to attend the Geneva talks on the currently decided dates under the present environment... It is the government that is creating a war-like situation and pushing us towards war," he told reporters.
But a Sri Lankan government minister, Rohitha Bogallagama, said he still expected the Tamil Tigers to attend talks at some stage.
"We are hopeful that they would be more realistic in terms of their decision and that we are hopeful that they will engage in peace talks with the government of Sri Lanka," he told the BBC Tamil service.
The Norwegian envoy met government officials in Colombo on Wednesday as part of his efforts to salvage the talks.
More than 60 people have died in bombings in Sri Lanka in the past week. The bodies of five Tamils were found near Jaffna on Wednesday.
Another five Tamils were killed in separate incidents by the military on Monday, the rebels say. The army denied the claim.
Surge in violence
Correspondents say the past week has been one of the bloodiest since the government and the rebels agreed a 2002 truce.
Peace talks, already postponed, had been due to take place on 24-25 April in Geneva.
The rebels put their participation in the talks on hold over the weekend, saying they would not go to Geneva until security measures had been eased, allowing them to hold crucial internal talks.
Reviving Sri Lanka's stalled negotiations is considered vital to strengthen a battered four-year ceasefire.
A surge in attacks in the north and east at the turn of the year abated after agreement was secured to hold talks in February, but violence has risen again in recent weeks.
The Tamil Tigers want autonomy for minority Tamils in the north and east of Sri Lanka. More than 60,000 people have died during two decades of conflict.