A powerful car bomb exploded yesterday near a military base used by Russian peacekeeping troops in Tskhinvali, the capital of the breakaway region of South Ossetia, killing at least seven and injuring three, writes Charles Clover in Moscow.

It was the worst act of violence since the end of the war in mid-August, and threatened a fragile peace accord in which Russia has pledged to withdraw its troops from positions in central Georgia and back to South Ossetia and Abkhazia by October 10. Russian officials said they were still investigating the blast. Some feared it could be used to justify any delay in the withdrawal.