Afghan security forces are battling insurgents who have launched a gun and bomb attack in the town of Tarin Kowt in Uruzgan province. Officials say the violence began with two suicide bombings outside official buildings, followed by fighting between gunmen and security forces in a market. At least two four are said to have been killed in the attack, which the Taliban said they carried out. Nato says it is providing air support to Afghan forces. Afghan intelligence officials told the BBC that the attack started when bombs exploded near the governor's office and the offices of a security firm owned by a local militia commander. Residents say heavy machine guns, rocket-propelled grenades and assault rifles are being used by both sides. Eyewitness Mohammad Dadu, a butcher at the market, told the BBC: ''I didn't have time to close my shop. I saw two dead bodies and four injured people with blood on their clothes." Afghan militants have stepped up their attacks as Nato troops begin the handover of security to local forces in parts of the country. On Wednesday the mayor of the volatile city of Kandahar was killed in a suicide attack. Two weeks ago, President Hamid Karzai's influential half-brother, Ahmad Wali Karzai, was killed in the same city.