Tamil supporters protest in London, Olso

By Nick Vinocur and Kate Kelland

LONDON (Reuters) - Hundreds of Tamil protesters demonstrated outside Britain's parliament on Tuesday calling for London's help in securing a ceasefire between Sri Lankan forces and Tamil Tiger separatists.

Police arrested four people after scuffles broke out when officers moved protesters off a major bridge into the square outside the Houses of Parliament.

In Oslo, several hundred Tamil protesters gathered outside the prime minister's office to demand help from Norway. Police blocked the entrance to the building. An aide to the prime minister met the protesters, a government spokeswoman said.

The London demonstration began on Monday, when 3,000 people -- some with young children -- began to occupy Westminster Bridge and the road leading to it alongside parliament's clock tower, popularly known as Big Ben.

Several hundred demonstrators stayed all night, blocking roads until police moved them in the early hours, and vowed to continue their protest. Two protesters jumped into the River Thames but were recovered by police boats and taken to hospital.

A police spokesman said there were around 600 to 700 protesters in Parliament Square, adding that officers were talking to protest leaders to help end the demonstration. Police said the demonstration was illegal.

The British Tamils Forum said the protest had been organized by Tamil students who fear thousands of civilians could be killed if the Sri Lankan military continues its offensive against the Liberation Tigers of Tamil Eelam (LTTE) in a no-fire zone in a northeastern coastal area.

"We are asking for a ceasefire between the Tamil Tigers and the government to end the civil war that has been going on for over 30 years," protester Mathithas Kandasamy, a 25-year-old student, told Reuters.

Foreign Secretary David Miliband said London was "very concerned at the plight of civilians caught up in the fighting."

"The need for a humanitarian ceasefire is now even more urgent," he said in a statement. "It is vital that civilians are able to move away from danger to safety."

The United Nations says tens of thousands of people are being held as human shields by the LTTE, and has urged the Sri Lankan military to protect them during a final offensive.

Palitha Kohona, permanent secretary at the Sri Lankan Ministry of Foreign Affairs, told BBC radio the government could not stop the offensive until LTTE agreed to lay down arms.

"The government wants to preserve the civilians, we want the civilians out, but the only decent thing that the LTTE can do now ... is to let the civilians go," he said. "The solution we have offered is very simple. LTTE must lay down its weapons, and then there will be no need to fire at anybody any more."

(Writing by Kate Kelland, editing by Alison Williams)

Terra/Reuters