The JVP, or People's Liberation Front, said the premier had also agreed to ditch a tsunami aid-sharing pact with the separatist guerrillas.

Rajapakse's election manifesto to be unveiled shortly would reflect the agreement, JVP leader Somawansa Amarasinghe told reporters.

Rajapakse, the presidential candidate of the ruling Sri Lanka Freedom Party, could not be reached while officials at his office and those managing his campaign said they had no comment.

"We have agreed to support the candidature of Prime Minister Mahinda Rajapakse for the presidency," Amarasinghe said. "We will sign the 12-point agreement in five to six days."

If ratified by the ruling party, which is led by President Chandrika Kumaratunga, the JVP's demands could lead to the complete overhaul of Norwegian-brokered peace efforts.

"It is hereby agreed to protect, defend and preserve the unitary nature of the Sri Lankan state under any solutions to be presented, formed or formulated for the purpose of the resolution of Sri Lanka's national question," said the purported agreement, copies of which were released to reporters.

The government and the Tamil Tigers agreed during their peace talks in December 2002 to work towards a federal solution and drop the unitary nature of the state as a way of ending ethnic bloodshed.

Those talks, however, have remained inconclusive since April 2003.

The JVP, which quit the coalition government in June in protest at the tsunami aid plan, said Rajapakse had also agreed to redraft a ceasefire agreement brokered by Norway and put in place in February 2002.

The ceasefire came under strain after the August 12 assassination of Foreign Minister Lakshman Kadirgamar, which the government blamed on the Tigers.