U.S. drones killed at least six militants in Pakistan on Sunday, according to local officials. A senior commander of the Pakistani Taliban reportedly died in the attack, which also injured four others. The militants had just returned from Afghanistan, where they were fighting coalition forces in the Paktika province. The attack, which occurred in a remote mountainous region known as the Valley that has long been a favorite refuge for Islamist groups like the Haqqani network, was the 15th CIA drone strike of the year in Pakistan. The attacks have rankled Pakistani officials, who say they violate their country's sovereignty.