A grenade exploded outside the home of a US diplomat in Georgia's capital late on Friday, an Interior Ministry spokesman said. The US diplomat's wife and child, who were the only people in the house at the time, were unhurt, said spokesman Guram Donadze. The grenade was thrown into the yard of the private house which is in an area near the centre of Tbilisi where many foreigners and diplomats live, he said. It was not clear who carried out the attack. The US embassy made no comment. Robberies and kidnappings of foreigners are common in Georgia, a mainly Christian ex-Soviet state of 5 million people, but there is no history of bombings targeting foreign citizens. Earlier this month three police were killed in a car bombing in the town of Gori, near the breakaway region of South Ossetia. President Mikhail Saakashvili said it was a terrorist act aimed at derailing peace talks with the region.