Tamils from across Europe demonstrated at the UN's European headquarters on Tuesday, calling for a probe into alleged war crimes committed by Sri Lanka at the end of the country's 2009 civil war.

According to local police, around 1,000 protesters gathered in Geneva's iconic Place des Nations, to urge the Human Rights Council to investigate the killing of tens of thousands of civilians by Sri Lankan forces in the final push of the country's brutal war against separatist Tamils.

"We want an international independent investigation" into the war crimes allegations, Kandiah Rajamanoharan, who had travelled from London to Geneva for the day, told AFP.

He added that the organisers were expecting between 5,000 to 10,000 demonstrators.

"And we are all for the independence of our Tamil homeland," he added.

Last week, UN leader Ban Ki-moon sent a report detailing similar allegations against Sri Lankan troops to the Human Rights Council, saying that he alone cannot order an inquiry into the killings but that a forum such as the UN's rights body could do so.

"We expect the United Nations to take up this issue," Rajamanoharan said.

Another demonstrator, Nivethan Nanthakumar who is still in high school and travelled from northern Switzerland, added that "two years after (the end of the conflict) the international community is doing nothing."

"We Tamils will not give up. We will fight for self determination, for freedom," he said.