LONDON - Thousands of Tamil protesters blocked streets outside Britain's parliament on Monday to demand a ceasefire between Sri Lankan government forces and Tamil Tiger separatists on the Indian Ocean island, a former British colony.

Large numbers of police were quickly deployed to contain the noisy but peaceful demonstration after it spilled out from the square in front of parliament to block several major streets on the opening day of a new parliamentary session.

Ex-patriate Tamils have mounted demonstrations against the conflict in cities across the world, but London has been a focus of protest as Britain, a former colonial power in Sri Lanka, is held responsible by Tamils for denying them their own land.

Members of Britain's Tamil population -- estimated to number around 200,000 -- have been demonstrating for two weeks, calling for an end to hostilities in Sri Lanka, where government troops have encircled Tamil fighters in the country's northeast.

The Sri Lankan government on Monday gave the guerrillas 24 hours to surrender after several thousand civilians managed to flee the war zone following weeks of intense fighting.

Government forces have repeatedly shelled the area where the Tamil fighters and many civilians are holed up, leading to accusations of indiscriminate killing. The International Crisis Group warned on Monday that a humanitarian tragedy was unfolding in the region, with around 150,000 civilians trapped.

For their part the Tamil Tigers, who have waged an armed struggle against the Sri Lankan government since the early 1980s, have used suicide bombers to attack government troops. A blast on Monday killed 17 people, including women and children, according to the Sri Lankan Defense Ministry.

FOG OF WAR

Angry demonstrators in London held aloft banners denouncing the conflict and describing it as a government-led genocide. Sitting on the road outside parliament or standing in groups with young children, they chanted for a ceasefire.

Hundreds of Tamil people are dying every day, we can't let this go on, said Sayan Selvaratnan, 29, who was given asylum in Britain eight years ago and whose parents remain in the north of Sri Lanka, an area Tamils want as their homeland.

We want a ceasefire to stop the killing. We have to do something to stop it. Police monitored the demonstration from afar and appeared inclined to let it die down naturally rather than breaking it up. Riot police were accused of brutality this month for their handling of G20 protests during which a man died.

Among the Tamil demonstrators is 28-year-old Subramanyam Parameswaran who has been on hunger strike for 14 days and says he will starve himself to death unless demands, including a ceasefire and U.N. intervention in the conflict, are met.

Protest leaders said they were determined to keep the demonstration going as long as was necessary to draw attention to their cause. Amid their fervor there also appeared to be misinformation about the conflict.

Virtually all those spoken to accused the government of using chemical weapons against the Tamils, but there is no evidence such weapons have been used. They also had wildly varying opinions on how many people had been killed.

One man said at least 1,000 civilians had been killed on Monday alone, while another standing a few feet away put the figure at 5,000.

An impassioned woman said she had heard it was 10,000, after government troops forced civilians to walk through a minefield and then gunned down those that refused to do it. Ten minutes later she returned to say it was actually 20,000 people.

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