Tehran: Iran's supreme leader Ayatollah Ali Khamenei vowed "severe revenge" after the United States killed the commander of the Islamic republic's Quds Force, General Qasem Soleimani, in Baghdad on Friday.

"Martyrdom was the reward for his ceaseless efforts in all these years," Khamenei said on his Farsi-language Twitter account in reference to Soleimani, also declaring three days of mourning.