Iran's supreme leader Ayatollah Ali Khamenei has called on Iraq to demand US troops leave "as soon as possible", warning that Washington is plotting to remove the Iraqi government.
The remarks came during a visit to Tehran on Saturday by Iraqi Prime Minister Adel Abdel Mahdi, whose country is under pressure from the United States to distance itself from Iran.
"You should take actions to make sure the Americans withdraw their troops from Iraq as soon as possible because wherever they have had an enduring presence, forcing them out has become problematic," Khamenei told Abdel Mahdi.
"The current government and parliament in Iraq and the political figures are not what the US desires; they plot to remove them from the political scene of Iraq," he said, according to his official website.
Abdel Mahdi, on his first official trip to Iran, also met Saturday with President Hassan Rouhani, who visited Iraq last month.
Baghdad is under pressure from Washington to limit ties with its neighbour, particularly after the United States withdrew from the Iran nuclear deal last year and hit Tehran with sanctions.
Iran has close but complicated ties with Iraq, with significant influence among its Shiite political groups.
The two countries fought a bloody war from 1980 to 1988 and Tehran's influence in Baghdad grew after the 2003 US-led invasion of Iraq toppled the government of Saddam Hussein.
Iran was the first country to respond to Iraqi calls for help after Islamic State group jihadists captured Mosul in 2014 and threatened to overrun Baghdad and Kirkuk.
Tehran dispatched "military advisors" and equipment overnight along with the Revolutionary Guards elite Qods Force commander Qasem Soleimani to prevent IS jihadists from approaching its western borders.
According to the Wall Street Journal, Washington is planning to designate the Revolutionary Guards as a terrorist organisation, an unprecedented move that would escalate tensions between the two countries.
The newspaper, quoting unnamed officials, said President Donald Trump's administration would announce the long-mulled decision as soon as Monday.
But it said that the Pentagon and the CIA were concerned the move would increase risks for US troops without doing much more to damage the Iranian economy.
Iran's parliament has vowed to retaliate by passing an urgent bill putting American troops on a terrorism blacklist alongside the Islamic State group, the semi-official news agency ISNA reported.
"Even though we believe one should not play along with America's extreme acts, the reality is that we must retaliate," the head of Iran's influential national security and foreign policy commission, Heshmatollah Falahatpisheh, told ISNA.
A statement signed by a majority of MPs in support of the bill said any action against Iran's national security and its armed forces was "crossing a red line" and the US administration would "regret" its decision.
The Islamic Revolutionary Guards Corp was formed after the 1979 Islamic revolution with a mission to defend the new system.
Designating the Guards as a terrorist organisation would "effectively be a service to terrorists," Falahatpisheh said, since they have "the biggest role in combatting terrorism" in the region.