MIR ALI, Pakistan – At least one suspected U.S. drone fired on a house in Pakistan's volatile tribal region Sunday, killing 20 people in the 11th such attack since militants in the area orchestrated a deadly suicide bombing against the CIA in Afghanistan, intelligence officials said. Four missiles slammed into the house in the Shaktoi area of South Waziristan, the same region where a drone strike Thursday targeted a meeting of militant commanders in an apparently unsuccessful attempt to kill Pakistani Taliban chief Hakimullah Mehsud. The militant leader helped organize the Dec. 30 attack against a remote CIA base in...