KANDAHAR, Afghanistan (AP) âÄî Four Taliban suicide bombers disguised in army uniforms detonated a car bomb and stormed a government office Wednesday, killing 13 people. The assault highlighted the increasingly deadly tactics that Taliban militants are learning from al-Qaida, an expert said. The multi-pronged raid mirrored an attack in Kabul in February when militants assaulted three government buildings simultaneously, killing 20. Wednesday’s attack on Kandahar’s provincial council office killed seven civilians and six police officers, President Hamid Karzai’s office said. Ahmad Wali Karzai, the head of the council and President Karzai’s brother, said the attack came during a meeting of tribal leaders. He said 17 people were wounded. The attack began just before noon, when a suicide bomber in a vehicle full of explosives blew himself up at the office gates, opening the way for three other attackers in Afghan army uniforms and AK-47s to storm the building, Ahmad Wali Karzai said. He told The Associated Press he was the target of the attack; he did not say how he knew he was the target. Gen. David Petraeus, the top U.S. general in the Mideast, said Wednesday that the Taliban and other insurgents are growing stronger and that the U.S. military will fight “relentlessly and aggressively” against extremists in Afghanistan and Pakistan. Al-Qaida and Pakistani militants are teaching advanced skills to the Taliban, and al-Qaida operatives are embedding with Taliban forces to “plus-up their capabilities,” said Bruce Hoffman, a terrorism expert at Georgetown University. “They’re graduating from, in essence, rural guerrilla warfare to sophisticated urban operations,” Hoffman said. “It’s skill sets that you’re not going to acquire on your own. It takes tutoring and mentoring. “So I think overall that this is a reflection of the Afghan Taliban’s skill set really being enhanced, both with their symbiotic relationship with jihadi elements across the border in Pakistan and with al-Qaida.” The Kandahar assault comes amid a burst of violence in Afghanistan, where some 60 militants have died in battles the last three days. President Barack Obama âÄî who is deploying an additional 21,000 U.S. forces to bolster the record 38,000 already in the country âÄî has said the U.S. will increase its focus on the “increasingly perilous” situation here. After the car bomb explosion, three militants wearing suicide vests and carrying assault rifles entered the Kandahar compound, said Interior Ministry spokesman Zemeri Bashary. Police killed two of the attackers and the third one blew himself up, he said. A fourth bomber died in the car bomb, bringing the overall death toll to at least 17. Among those killed were the province’s education director and its deputy health director, Ahmad Wali Karzai said. The president’s brother said he left the council office about five minutes before the attack and was not harmed. Qari Yousef Ahmadi, a Taliban spokesman, claimed responsibility for the assault and said the target was the provincial compound. The Kandahar attack came as the Interior Ministry announced that Afghan police and coalition forces killed 31 militants in a neighboring province, the second large battle in the Afghan south in two days. The fight took place in three villages in the Kajaki region of Helmand on Tuesday. Kajaki is the site of a U.S.-funded dam that provides hydroelectric power to much of southern Afghanistan. The dam is protected by British troops in an area surrounded by hostile militants. The Afghan government admits it has little control in that part of Helmand, the world’s largest opium poppy-growing region. In Uruzgan province on Monday, Afghan and foreign troops killed 30 Taliban fighters, police said. Militant attacks have grown increasingly deadly the last three years, and insurgents now control wide swaths of countryside where Afghan and international forces don’t have enough manpower to maintain a permanent presence. ___ Associated Press reporter Jason Straziuso reported from Kabul.