Waving the red flag of Tamil Eelam, the protesters chanted "Stop the genocide!" and "Stop the war!" for a second day as police hemmed them in at Parliament Square across the street from the Houses of Parliament in central London, CNN reported.
Police said that one point during the demonstration, the protesters blocked the street leading to Westminster Bridge, necessitating road closures around Parliament.
The demonstrators espoused support for Liberation Tigers of Tamil Eelam rebels, who have fought the Sri Lankan government since 1983 for an independent homeland for the island nation's ethnic Tamil minority. Government forces have encircled the remnants of the LTTE's force in a small area designated as a civilian safe zone.
"The Sri Lankan government has now cornered the rebels, the LTTE, and what they are doing is killing the people," protester Dushyanthy Sukumar told CNN.
Another demonstrator, Hariram Shan, 24, told the U.S. broadcaster they hope to sway Britain to intervene in what they say is the killing of Tamil civilians by the Sri Lankan military.
Exploding whale video goes viral on Internet
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'