Secret intelligence files held by Yemeni security forces and containing details of American intelligence operations in the country have been looted by Iran-backed militia leaders, exposing names of informants and plans for U.S.-backed counter-terrorism operations, U.S. officials say. U.S. intelligence officials believe additional files were handed directly to Iranian advisors by Yemeni officials who have sided with the Houthi militias that seized control of the capital of Sana last September and later toppled the U.S.-backed president. For American intelligence networks in Yemen, the damage has been severe. Until recently, U.S. forces deployed in Yemen had worked closely with President Abdu...