Two American B-52 bombers flew another show-of-force mission in the Persian Gulf on Wednesday, a week after President Trump warned Iran that he would hold it accountable "if one American is killed" in rocket attacks in Iraq that the administration and military officials blamed on Tehran. The warplanes' 36-hour round-trip mission from Minot Air Force Base in North Dakota was the third time in six weeks that Air Force bombers had conducted long-range flights about 60 miles off the Iranian coast, moves that military officials said were intended to deter Iran from attacking American troops in the region. The United States periodically conducts such quick demonstration missions to the Middle East and Asia to showcase American air power to allies and adversaries. But tensions have been rising in advance of the Jan. 3 anniversary of the American drone strike that killed Maj. Gen. Qassim Suleimani, the commander of Iran's elite Quds Force of the Islamic Revolutionary Guards Corps, and the Iraqi leader of an Iranian-backed militia -- deaths that Iranian leaders repeatedly insist they have not yet avenged.