Thousands of protesters are blocking roads around the Houses of Parliament in central London to try to get Britain to help stop the war in Sri Lanka.
Conflict is raging in the north of the country in Asia, between the Sri Lankan government and a group who are against them, called the Tamil Tigers.
About 100,000 ordinary Tamil people are thought to be trapped in the area where the fighting's happening.
Demonstrators in the UK want Britain to do more to demand a ceasefire.
On Monday, several roads in London had to be shut as police struggled to contain about 3,500 protesters.
It's the latest in a series of demonstrations that have been staged in the capital over the past two weeks.
The Sri Lankan government has rejected calls for a ceasefire, saying it would give the Tamil Tigers time to regroup.
The Tigers are fighting for their own separate state in the north and east of Sri Lanka.
The conflict has been going on for almost 30 years. Norway helped to arrange the last ceasefire in 2002, but that was broken at the beginning of 2008.