COLOMBO: Sri Lanka’s president has ordered the release of his jailed electoral rival, ex-army chief Sarath Fonseka, bowing to US-led international pressure three years after the end of the island's long ethnic war.

The 61-year-old former four-star general could leave prison on Monday following legal formalities, an official said Sunday, after President Mahinda Rajapakse marked the third anniversary of the Tamil Tigers’ crushing defeat.

Fonseka was arrested two weeks after he unsuccessfully challenged Rajapakse’s re-election in January 2010.

“President signed the papers (ordering Fonseka’s release) on the 18th evening... before leaving for Qatar (on Saturday),” spokesman Banda Jayasekera said.  “Papers will be sent to the Ministry of Justice on Monday.”

Fonseka's wife Anima Fonseka said she welcomed the latest decision to release her husband but was unaware of the terms of the presidential pardon.

“I welcome the announcement (of the release),” Anima Fonseka told reporters outside a private hospital where prison authorities took her husband for treatment for a respiratory problem two weeks ago.

“I hope the president will keep his promise to release him unconditionally,” Anima Fonseka said, adding that she hoped there would be no legal impediment for him to engage in politics.

However, official sources said the pardon only remits the sentence and Fonseka may not have his civic rights to participate in elections for seven years from the time he walks out of jail.

Fonseka is credited with leading the military campaign that crushed the Tamil Tiger rebels in May 2009, but also encouraged international calls to probe the alleged deaths of up to 40,000 civilians in the war’s final months.

The once feared Fonseka was regarded by the United States as a political prisoner and Washington had repeatedly called for his release.

President Rajapakse issued the release order after his foreign minister, Gamini Lakshman Peiris, met in Washington on Friday with US Secretary of State Hillary Clinton for talks on the island’s human rights record.

Clinton believed that Sri Lanka has put forward “a very serious” plan for reconciliation after its civil war, and urged the government to move forward on protecting human rights, the State Department said.

The US had asked Sri Lanka to improve press freedom and human rights, and also “de-militarise” the former war zone in the island's north. But Rajapakse, in an address to the nation Saturday, ruled out a troop withdrawal.

In the speech marking the victory anniversary, Rajapakse made no reference to his erstwhile military chief, who has been stripped of his rank and pension by a court martial.

Fonseka fell out with Rajapakse over who should take credit for ending the savage ethnic bloodshed which killed up to 100,000 people between 1972 and 2009.

He had also angered the government by saying he would gladly testify before any international tribunal probing possible war crimes charges, after the UN said thousands of civilians were killed in the last months of fighting.

Fonseka was initially jailed for 30 months in September 2010 by a military court for corruption relating to military procurements.

In November 2011, he was sentenced to three more years in jail for saying that surrendering Tiger rebels had been killed on the orders of the president's brother Gotabhaya Rajapakse, who is the defence secretary.

Sri Lanka has denied that any civilians at all were killed by its troops at the climax of the war.