U.S. and Afghan troops have advanced into the Taliban heartland in southern Afghanistan in the first major offensive after U.S. President Barak Obama's Wednesday announcement of troop surge in the insurgency-ridden country. The operation dubbed "Cobra's Anger", began yesterday in the Nawzad district of Helmand province. It involves some 1,000 U.S. Marines and 150 Afghan soldiers to disrupt Taliban supply and communications lines in the region. In a statement, the Afghan Defense Ministry today said so far four militants have been killed and two were detained and addded that the operation is scheduled to last for four days. Nowzad is one of the hotbeds of hard-core Taliban militants in Helmand known as the Taliban safe haven and notorious for growing poppy in Afghanistan.least 13 militants were killed and two commanders arrested today in the ongoing military operation in different parts of Pakistan. Local media report said backed by helicopter gunship, security forces bombed militants' hideouts in Orakzai tribal agency killing seven militants and injuring 11 others. In aerial strikes, three vehicles and five hideouts of Pakistan Taliban chief Hakimullah Mehsud's aides were also destroyed. According to military sources, two close associates of Baitullah Mehsud, the slain chief of Tehreek-e-Taliban Pakistan ( TTP), were arrested in Hangu, a city adjoining Orakzai.Meanwhile, the security forces claimed to have killed as many as six more extremists and injured eight others in fresh fierce clashes with militants in parts of South Waziristan tribal area this morning. As many as 20 suspected persons were arrested during search operation in Swat valley in North West Frontier Province. Arms and ammunitions including a rocket and 16 Kalashnikovs were also recovered from the restive area.