Parliament completes its six-year term on April 22 and the new parliamentary election should be held within 6-8 weeks from the date it is dissolved, according to the island nation's parliamentary election act.
Incumbent Mahinda Rajapaksa beat former army commander General Sarath Fonseka by a landslide in last month's presidential election.
After losing the poll, Fonseka accused his former commander-in-chief of vote-rigging, vowing to challenge the results in court and stand for parliament.
Troops arrested Fonseka, who quit the army in November to enter the presidential race, and the government said he would be court-martialled on charges of conspiring against the president.
Under Sri Lankan military law, the armed forces can arrest and try personnel who have left service for up to six months after their departure, defence spokesman Keheliya Rambukwella told a press conference.
Still investigations are going on and information is emerging from the investigations, he said.
Sri Lanka's Government Information Department on Tuesday said Fonseka's comments to reporters, quoted by the BBC, that he would testify in a war crimes probe proved his disloyalty to the troops he led to defeat the Tamil Tigers rebels and end a 25-year war.
This report of BBC confirms beyond doubt that the retired general was hell-bent on betraying the gallant armed forces of Sri Lanka who saved the nation from the most ruthless terrorist group in the world, the statement said.Opposition politicians who backed Fonseka's election bid condemned his arrest, and vowed to seek legal redress.
To all of us it is evident that this is a government which is not simply dictatorial but fascist and they are all out to humiliate him, harass him and go on a journey of vendetta, Sri Lanka Muslim Congress leader Rauff Hakeem told reporters.
The general had stood side-by-side with Rajapaksa in May after the Tamil Tigers' defeat, but fell out later over what he said was false accusations of planning a coup and a promotion he complained had sidelined him by stripping his powers.
He then became the common candidate of several weakened opposition parties with divergent ideologies, who united solely for the purpose of beating Rajapaksa. Some of the parties had earlier criticised him sharply for his conduct of the war.
I can't see the purpose being served because it sort of turns up the pro-Fonseka elements once again to vigorously take up his cause, said Col. R. Hariharan, an analyst and retired Indian army intelligence officer who served in Sri Lanka.
The powers that be are not in a mood to forgive.
The campaign turned bitter and personal, with Fonseka and Rajapaksa trading allegations of corruption and misconduct.
(Writing by Bryson Hull; Editing by Jeremy Laurence)