Sri Lankan Prime Minister - and presidential election candidate - Mahinda Rajapakse has signed a deal with the Sinhala nationalist JVP.
President Chandrika Kumaratunga opposes the agreement
The pre-poll deal includes a commitment to retain a unitary state in Sri Lanka, redraft a ceasefire with Tamil Tigers and to stop privatisation.
In return the JVP, who pulled out of the government this year complaining about concessions to the Tigers, will support Mr Rajapakse's election bid.
Elections are due by the end of 2005.
"It is agreed to protect, defend and preserve the unitary nature of the Sri Lankan state under any solution to be presented, formed or formulated for the purpose of the resolution of the national question," the agreement states.
The deal is strongly opposed by the incumbent president Chandrika Kumaratunga, who comes from the same party - the Sri Lanka Freedom Party (SLFP) - as Mr Rajapakse.
Ms Kumaratunga, who attracted the ire of the JVP after agreeing a deal to share post-tsunami aid with the Tigers, said on Wednesday that she would not "throw away 11 years of work in a mere election promise".
The deal signed on Thursday also commits Mr Rajapakse, if elected, to scrap the post-tsunami aid-sharing deal.
But senior members of the SLFP have said that the deal signed on Thursday is not 'final'.
Alavi Moulana, deputy leader of the SLFP and governor of the Western Provincial council, told the BBC Tamil service that the deal could be "re-evaluated, re-analysed".
"What has been agreed," he said, "are personal wishes and opinions...no one can be objecting to personal wishes".
Prime Minister Rajapakse rejected criticisms that the agreement, signed formally on Thursday after an earlier verbal agreement, could lead back to war with the Tamil Tigers.
"This agreement will not lead to war but peace, prosperity and development for all," he said.
Leader of the JVP - or People's Liberation Front - Somawansa Amarasinghe said that his party were not afraid of war.
"You can't bring peace by being afraid of war," he said.
The elections have been prompted by a Supreme Court ruling stating that President Chandrika Kumaratunga's term ends in December.
Under the constitution, she is barred from contesting a third term.
President Kumaratunga was at the helm during six rounds of peace talks with the Tamil Tigers.
Those talks broke down in 2003, but before then both sides had made an unprecedented agreement to work towards a federal solution of the conflict on the island.
Mr Rajapakse's main opponent in the presidential elections is former Prime Minister Ranil Wickremesinghe.
Mr Wickremesinghe is campaigning on a platform of reviving the peace process with the Tigers and continuing policies of economic liberalisation.
More than 60,000 people have been killed in Sri Lanka since the Tamil Tigers launched their campaign for a separate Tamil state in the north and east of the island in 1983.