BAGHDAD (AP) - Iran has vowed ``harsh retaliation'' for a U.S. airstrike near Baghdad's airport that killed its top general and the architect of its interventions across the Middle East.

The killing of Gen. Qassem Soleimani, the head of Iran's elite Quds Force, marks a major escalation in the standoff between Washington and Iran.

Iran's supreme leader warned that a ``harsh retaliation is waiting'' for the U.S. after the airstrike, calling Soleimani the ``international face of resistance.''

The killing, and any forceful retaliation by Iran, could ignite a conflict that engulfs the whole region, endangering U.S. troops in Iraq, Syria and beyond.

The U.S. ordered its citizens to leave Iraq and closed the embassy in Baghdad.