Police and protesters clash in Sri Lanka

Opposition MPs vow to impeach Kumaratunga in a bid to stop the country sliding into dictatorship

COLOMBO, Sri Lanka -- Police and protesters have exchanged tear gas and rocks as thousands poured into Colombo to protest at the suspension of Sri Lanka's parliament.

Despite a police ban and arrest warnings, more than 15 parties from across the political spectrum aimed to cripple the capital with tens of thousands of supporters on Thursday.

Witnesses said teargas was fired to try to disperse a crowd of several thousand heading into Colombo from the beach and fishing resort of Negombo to the north, one of six marches planned to converge on the center.

"We have to go ahead regardless of what the police do," said Karu Jayasuriya, deputy leader of the main opposition United National Party (UNP).

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"This is a political attempt to suppress opinion opposite to that of the government."

Police placed large vehicles across several roads to block the marches.

The demonstrations are the latest in a series of confrontations between the government and the opposition since the ruling party lost its majority in parliament.

President Chandrika Kumaratunga suspended the legislature to thwart a no-confidence vote after a key Muslim ally defected and plunged the country into uncertainty.

Underscoring the political volatility of the country, a series of explosions destroyed an office of the Muslim party on Wednesday and Sri Lankan air force jets bombed a flotilla of boats belonging to Tamil Tiger guerrillas.

The unrest has prompted the United States to warn its citizens not to travel to the small island nation.

Kumaratunga has called for a national referendum on August 21 to get backing for constitutional changes to help end the country's ethnic war and to change the electoral system.

But opposition members of parliament have been defiant and vowed to impeach her.

Civil unrest

Fighting has intensified around the key northern city of Jaffna

While Sri Lanka has been beset by civil war for nearly 18 years, with more than 63,000 people dying in the drawn-out battle with Tamil rebels, the deepening political crisis has added fuel to the fire.

The situation has got so bad that the United States has warned its citizens to stay away as opposition parties mount a campaign of peaceful civil unrest beginning mid-July.

"It appears Sri Lanka may be entering a period of increased civil unrest and mass political demonstrations," the U.S. announcement said in its advisory.

Three devices exploded before dawn at the Sri Lanka Muslim Congress office in the eastern town of Kalmunai, destroying the building but causing no casualties.

The largely Muslim town of Kalmunai, east of the capital, has been tense since seven Congress members of parliament crossed the floor of the legislature last month depriving the government of its majority.

Four other Congress members stayed with the government and the two factions have faced off in a series of increasingly violent protests and strikes, particularly in the aftermath of parliament's suspension.

The pro-opposition faction has accused police of heavy-handed tactics to quell their protests, and demanded an investigation into the deaths of two school boys during a demonstration last week.

Black market arms

Recruits are always needed in this drawn-out civil war.

Kalmunai, the stronghold of the Muslim Congress, is part of Sri Lanka's North East Province where Tamil Tiger rebels have been fighting for separate state since 1983.

Adding to the country's woes, air strikes were ordered on the Tigers after a naval patrol stumbled on a rebel supply convoy of eight boats, they said.

The rebels buy their arms and ammunition on the international black market and usually use small boats to smuggle the supplies on to the island.

A Norwegian-brokered initiative to end the conflict has been stalled for months over conditions for peace talks.

Reuters contributed to this report.