The U.S.-led NATO force in Afghanistan killed al-Qaida's second-highest leader in the country in an airstrike in eastern Kunar province, the coalition said Tuesday. Many senior al-Qaida commanders have died in U.S. drone attacks in Pakistan's northwest tribal region, and bin Laden was killed by U.S. commandos in the Pakistani town of Abbottabad last May. Bin Laden advised al-Qaida militants to leave Pakistan's North and South Waziristan tribal areas because of the threat of drone attacks, according to letters seized from the compound where he was killed. The documents were later released by the U.S. In one of the letters, bin Laden recommended they go to Afghanistan's Kunar province because of "its rougher terrain; too many mountains, rivers, and trees that can accommodate hundreds of brothers without being spotted by the enemy," according to the Combating Terrorism Center at West Point, which published the documents.