Iranian Supreme Leader Ayatollah Ali Khamenei on Wednesday called an overnight missile strike on military bases, where U.S. troops are stationed in Iraq, a "slap across the face of the United States."
Iran TV said none of the 35 missiles launched had been intercepted and claimed the attack resulted in 80 casualties.
U.S. officials said that the Pentagon “had no confirmation” that any Americans had been killed.
Warning the U.S. at a ceremony commemorating slain General Qassem Soleimani, Khamenei said the United States may have "cut off Soleimani's arm" but Iran will respond by "cutting off your legs" in the region.
The Iranian general was assassinated in a U.S. drone attack on his convoy near Baghdad Airport on Friday.
Khamenei went on to say the U.S. was trying to remove Hezbollah from Lebanon in a bid to help Israel, but the Iranian-backed militia is acting as "our hands and eyes."
Iranian Foreign Minister Mohammad Javad Zarif on his Twitter account said that the Islamic Republic seeks neither escalation or war, but "will defend ourselves against any aggression."
On Iranian television, Zarif said that Tehran's missile attack was "legitimate self-defense."
The Revolutionary Guard Corps said they would not hesitate to strike American military bases elsewhere in the region and added that the "Zionist entity" is not removed from the United States in the crime committed against Iran.