Police say the number of protesters has dwindled overnight
A Tamil protest in central London has entered a third day, although police say only about 25 demonstrators remain at Parliament Square.
More than 3,000 people have taken part in the rally since Monday afternoon, calling for the UK government to act to help end war in Sri Lanka.
Seven people were arrested during clashes with police, who have been trying to bring the protest to an end.
The Tamils have insisted they will remain until a cease-fire is called.
They say the thousands of civilians in northern Sri Lanka are in danger as its government continues an offensive to "wipe out" the rebel Tamil Tigers group.
Police say the demonstrators' action is unlawful because they did not give notice of the rally, which led to the closure of Westminster Bridge at its height.
A Metropolitan Police spokesman said officers had negotiated with community leaders throughout Tuesday to bring the rally to an end without making large numbers of arrests.
Police tackle protesters at Westminster
These efforts had failed, despite the backing of MPs.
"An operation has been put in place around those remaining in Parliament Square to ensure that disruption to London is kept to a minimum and the protest remains static within the square for participants' own safety," the spokesman added.
However, the Met said the number of protesters had fallen from about 400 to 25 by Wednesday morning.
Trouble had flared earlier as scores of officers moved hundreds of demonstrators off the roads and into Parliament Square.
There was some pushing and shoving and reports suggested that, after one surge, three people were taken away on stretchers after cans and a stick were thrown.
Some demonstrators were treated for minor injuries.
Police had issued "repeated requests" for flags bearing images representing the Tamil Tigers - a banned group in the UK - to be removed.
The need for a humanitarian ceasefire is now even more urgent - it is vital that civilians are able to move away from danger to safety
Foreign Secretary David Miliband has insisted the government was "very concerned" about civilians caught up in fighting in Sri Lanka.
He described reports suggesting the Sri Lankan military were fighting inside a 'no-fire zone', where the civilian population is concentrated, as "deeply worrying" and said the need for a ceasefire was "even more urgent".
In recent weeks, the clashes between security forces and Tamil Tigers have intensified as the security forces enter what they say is a final push to defeat the rebels and end nearly three decades of conflict.
The United Nations says more than 2,800 civilians may have been killed and 7,000 others injured in the fighting in the north-east in the last two months. The Sri Lankan government disputes these figures.
Leicester East MP Keith Vaz said he would deliver a letter to Downing Street on Wednesday calling for the situation to be debated by the UN Security Council, signed by a number of Labour and Lib Dem MPs.
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