Iranian Foreign Minister Javad Zarif harshly reacted to the killing of Qasem Solaimani, commander of the Iranian Revolutionary Guards' Quds Forces in a U.S. drone strike in Iraq.
"The U.S.' act of international terrorism, targeting & assassinating General Soleimani -- THE most effective force fighting Daesh (ISIS), Al Nusrah, Al Qaeda et al -- is extremely dangerous & a foolish escalation. The US bears responsibility for all consequences of its rogue adventurism," Zarif wrote on Twitter.
Mohsen Rezaee, a former Revolutionary Guard commander, also said on Twitter that Iran will "take a bitter revenge from the U.S."
The strike near Baghdad International Airport also killed Abu Mahdi al-Muhandis, vice president of the Hashd al-Shaabi group, or Popular Mobilization Units (PMU).
The attack came amid Iranian tensions with the U.S. after thousands of Iraqis stormed the U.S. Embassy compound on Tuesday, protesting against Sunday airstrikes in Iraq and Syria against the Kataib Hezbollah militia which killed 25 of its fighters.
The airstrikes were in response to a Friday rocket attack on a U.S. military base in Kirkuk blamed on Kataib Hezbollah, which is part of the Iran-backed Hashd al-Shaabi group.
Friday's attack killed one U.S. contractor and wounded four U.S. service members.
Soleimani was the long-time commander of the Quds Force, which has been designated as a terror group in the U.S. since 2007. The group is estimated to have 20,000 members.
Shortly after the reports on the slain military leaders, U.S. President Donald Trump posted the U.S. flag on Twitter with no comment.
The Pentagon accused Soleimani of planning to carry out attacks on U.S. diplomats and service members in Iraq and the region, saying the slain leader was responsible for the deaths of hundreds of Americans and coalition service members.
By Gozde Bayar
Servet Gunerigok in Washington contributed to this story