WASHINGTON - Sri Lanka was hit by sharp international criticism as troops arrested the defeated opposition candidate, just two weeks after an election that had raised hopes of turning a new page.

The United States voiced worries that the arrest late Monday of former general Sarath Fonseka would worsen divisions on the island, which last year emerged from a bloody 37-year ethnic war.

"We are following the situation closely and we have concerns that any action be in accord with Sri Lankan law," State Department spokesman Philip Crowley told AFP.

"There is a tremendous need for the government of Sri Lanka to work to overcome the fissures that exist within its society," he said.

"It has to be very cautious that any actions it takes are designed to heal the split within Sri Lankan society, not to exacerbate it," he said.

Sri Lankan state media said Fonseka, a former army general who led the campaign that killed the leadership of the Tamil Tiger rebels, would be charged with unspecified "military offenses."

Hours earlier, Fonseka said he would testify before any tribunal on alleged war crimes - an idea fiercely opposed by President Mahinda Rajapakse's government.

Western nations had voiced guarded hope at improving relations with Sri Lanka after the January 26 election.

It was the first vote since the rout of the Tigers, who waged a ruthless campaign for a separate homeland for the island's Tamil minority.

Rajapakse and Fonseka had both claimed credit for defeating the Tigers.

But Fonseka in particular reached out to Tamil voters in hopes they could tip the race between the two members of the Sinhalese majority.

"Whatever the government does has implications for how democratic institutions are perceived in the future," Crowley said.

"It's an unusual action to take right on the heels of an election," he said of the arrest.

Fonseka holds US residency, although officials said it did not affect their treatment of him.

Another official in Washington told AFP that US diplomats had been working behind the scenes to encourage Rajapakse to be cautious, warning that an arrest of Fonseka without legal grounding would have serious effects on relations.

The United States believed that the election was free, credible and - by regional standards - peaceful, but "we have been very disturbed by developments since the election," the official said.

On Friday, diplomats said that the European Union had decided to suspend preferential trade status to Sri Lanka - a major source of garments - because of its human rights record.

The Tamil diaspora has pushed Western nations to take a harder line with Sri Lanka, leading Rajapakse's government to turn increasingly on nations such as China and Iran for support.

One community leader in Canada, which has the West's most politically active Tamil diaspora, hoped that Fonseka's arrest would lead to renewed pressure on Sri Lanka.

"If they can court-martial a top general who polled about 40 percent in a presidential election, that means they can do anything to a Tamil citizen," said David Poopalapillai, national spokesman for the Canadian Tamil Congress.

"The carrots-and-sticks approach that the international community has been following has to be put to an end," he said.

"The time has come to go strong on this country and bring some diplomatic and economic sanctions."

Amnesty International said the election had offered Rajapakse a chance to improve human rights.

"Instead, we're seeing less and less tolerance for criticism," said Sam Zarifi, Amnesty International's Asia-Pacific director.