The announcement on a rebel-affiliated website said on Thursday the group had told Norwegian peace envoy Jon Hanssen-Bauer they would not be able to attend the talks scheduled for April 24 in Switzerland.
"Until a stable and conducive environment is created, we will not be able to attend the talks," the statement said.
Earlier Bauer had travelled to the north of the country for talks with Tamil leaders aimed at pulling the country back from a return to civil war.
The visit has been overshadowed by weeks of spiralling violence.
Over the past two weeks about 80 people have been killed in a series of suspected Tiger attacks, ethnic riots and an increasing number of unsolved murders that the government and rebels blame on each other.
On Thursday another four people were reported killed in a series of attacks and clashes across the country.
In one incident suspected members of the Liberation Tigers of Tamil Eelam (LTTE) shot and killed a rival activist in the eastern town of Batticaloa on Thursday, while rebel forces also engaged in a gun battle with government forces in the neighbouring district of Trincomalee, a defence official said.
The body of a suspected LTTE member was found together with a hand grenade at Kinniya in Trincomalee, an official said, adding that a government soldier was wounded in the firefight.
Two more dead bodies were found at Maharambakulam in Vavuniya district, the military said, but their identities had not been established.
Spriralling violence is threatening
a return to civil war
The Tigers say they will not go to Geneva until they can meet their eastern rebel commanders for a meeting.
But they pulled out of a previous scheme by Nordic ceasefire monitors to escort them by land and sea and have yet to accept a government offer to use private helicopters for the transport.
The government said on Wednesday the offer of helicopter transportation would only last another 72 hours.
The Tigers have also said they want killings of ethnic Tamil civilians to stop before they go to talks.
If the talks do not take place, most expect recent violence - the worst since the ceasefire was signed - to increase, and fear it could lead to a new war on an island still struggling to recover from years of conflict and the effects of the 2004 tsunami.