"We have informed the government that we are withdrawing our support to the government with immediate effect'', People's Liberation Front (JVP) leader Somawansa Amarasinghe told reporters Thursday.
The two coalition partners disagreed over a proposed deal with Tamil rebels on aid distribution in the north and eastern parts of the country following the devastating December 26, 2004 tsunami.
An estimated 40,000 people were killed in Sri Lanka and another one million were displaced by the December 26 tsunami that devastated nearly two thirds of the country.
The withdrawal of the 39 JVP members from the coalition will leave the UPFA government with only 89 members, far below the minimum of 113 members of parliament to maintain a stable government.
But the country's main opposition United National Party (UNP), which has 68 members, and the Tamil National Alliance, which has 22 members, have agreed to prevent the immediate collapse of the government.
The coalition government was formed in April last year after President Chandrika Kumaratunga dissolved the UNP-led government and called for fresh elections.
The Marxists have had several confrontations with President Kumaratunga including issues on privatizing the electricity and petroleum sectors, but the dispute over the proposed deal with Tamil rebels was seen as the climax.
President Kumaratunga planned to give the Liberation Tigers of Tamil Eelam (LTTE) a say in the distribution of aid in Tamil areas.
The Tamil Tigers have been fighting for autonomy for the Tamil minority in the areas where they live. The two-decade-old conflict has cost 69,000 lives.
The president said the proposed deal is necessary for the smooth distribution of aid to the rebel-held areas effected by the tsunami last year.
JVP said that Kumaratunga was legitimizing the LTTE with the plan and told her to withdraw it by Thursday. She refused, seeing the fact the rebels wanted to cooperate with the government as an opportunity.
The government and the Tamil Tigers have maintained a fragile ceasefire for three years. Peace negotiations have been put on ice.
In recent weeks violent clashes have been increasing in number, especially in the east of the county, Sri Lanka Monitoring Mission (SLMM) head Hagrup Haukland told Deutsche Presse-Agentur dpa.
"It isn't a serious threat to the ceasefire, we hope,'' Haukland said.
The violence has led to "uncertainty, frustration and a poisoned atmosphere'', Haukland said, but he believed that peace talks would nonetheless resume. dpa ad me wjh sc
- Deutsche Presse Agentur
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