Some 200 people gathered outside each of the two countries' missions to demonstrate against the ongoing violence in Sri Lanka, where Tamil Tigers are vowing to make a final stand against government forces.
Extra police were drafted in after "an incident occured at the Indian High Commission, which has resulted in some damage to the building," said a Scotland Yard spokeswoman.
Three arrests were made there for criminal damage, while outside Sri Lanka's High Commission there were also three arrests -- one for criminal damage, one for violent disorder and one for a public order offence, she said.
There was no immediate comment from the Indian diplomatic mission, where smashed windows were clearly visible.
The Sri Lankan fighting has sparked a wave of international concern for the fate of 50,000 people still said by the United Nations to be trapped in the conflict zone.
The UN also estimates that as many as 6,500 civilians may have been killed and another 14,000 wounded in fighti