Iran said Thursday it "only acts in self-defence" after President Donald Trump warned it and its allies against attacking US troops in Iraq.

"Unlike the US -- which surreptitiously lies, cheats & assassinates -- Iran only acts in self-defence," Foreign Minister Mohammad Javad Zarif tweeted.

"Don't be misled by usual warmongers, AGAIN," he wrote, also cautioning that "Iran starts no wars, but teaches lessons to those who do".

Tensions have risen sharply between Tehran and Washington ever since Trump withdrew from a landmark nuclear agreement and reimposed sweeping sanctions in 2018. They escalated in January when the US killed Iran's Major General Qasem Soleimani in a Baghdad drone strike, following attacks on its troops in Iraq that Washington blamed on Iran-backed armed groups.

Iran retaliated by firing at bases in Iraq housing US troops. Trump warned Iran on Wednesday that it would pay a "heavy price" in the event of further attacks on US troops.

He tweeted that "upon information and belief, Iran or its proxies are planning a sneak attack on U.S. troops and/or assets in Iraq." In response, Zarif wrote on Twitter that "Iran has FRIENDS: No one can have MILLIONS of 'proxies'"

Iran and the US are in a tense battle for influence in Iraq, where Tehran has powerful allies and Washington has close ties to the government. Bases housing US troops and foreign embassies, particularly the American mission, have been targeted in more than two dozen rocket strikes since late October.

The attacks, which the US has blamed on Iran-backed armed groups, have prompted fears of a proxy war on Iraqi soil.