WASHINGTON (AP) — Two American bomber aircraft have flown over a swath of the Middle East, sending what U.S. officials call a message of deterrence to Iran. The flight of the B-52H Stratofortress bombers over the region Thursday was the second such mission in less than a month. It was designed to underscore America’s commitment to the Middle East despite troop withdrawals from Iraq and Afghanistan. U.S. officials also are worried about a possible Iranian retaliatory strike on the anniversary of the U.S. airstrike that killed Iran’s top general near Baghdad’s airport last January. The long-range heavy bombers flew out of Barksdale Air Force Base in Louisiana on Wednesday. Adversaries often deem them a provocative show of force.