President Donald Trump has warned Iran of a "heavy price" if it or its allies in Iraq attack U.S. troops or assets in Iraq.
"Upon information and belief, Iran or its proxies are planning a sneak attack on U.S. troops and/or assets in Iraq," Trump tweeted on April 1.
"If this happens, Iran will pay a very heavy price, indeed!" he added.
It was not immediately clear if Trump meant the United States actually has intelligence of such a plan.
Over the past year, the United States has accused Iranian-backed militias of attacks on Iraqi military bases hosting coalition forces and on foreign embassies, particularly the U.S. mission.
Hours before Trump's tweet, a top military aide to Iranian Supreme Leader Ayatollah Ali Khamenei cautioned the United States of consequences of "provocative actions" in Iraq.
"Any U.S. action will mark an even larger strategic failure in the current president's record," General Yahya Rahim Safavi said, according to the semiofficial news agency Tasnim.
On March 11, a rocket attack on an Iraqi base killed two U.S. troops and one British soldier, heightening tensions in the region.
No one claimed responsibility for the attack, which was followed by deadly U.S. air strikes on the pro-Iranian Kataib Hezbollah militia group.
Tehran warned Trump against taking "dangerous actions."
In December, Washington blamed Kataib Hezbollah for a strike that killed a U.S. contractor and triggered a round of violence that led Trump to order the killing of a top Iranian general, Qasem Soleimani, in a drone strike in Baghdad the following month.
In retaliation, an Iranian ballistic-missile strike on an Iraqi air base left some 110 U.S. troops suffering from traumatic brain injuries.