A senior Iranian Revolutionary Guard commander urged Iraqi Shi'ite militias to step up attacks on US targets during a meeting in Baghdad last week, three militia sources and two Iraqi security sources familiar with the gathering said, Reuters reported.
American forces in Iraq and Syria were attacked several times following the visit by an Iranian delegation led by Revolutionary Guards intelligence chief Hossein Taeb, which came after deadly US air strikes against Iran-backed militias at the Syrian-Iraqi border on June 27.
While encouraging retaliation, the Iranians advised the Iraqis not to go too far to avoid a big escalation, three militia sources briefed on the meeting said.
The Iranians did, however, advise them to widen their attacks by retaliating against US forces in Syria, according to one of the three militia sources, a senior local militia commander briefed on the meeting.
The flare-up comes as significant differences cloud diplomatic efforts to revive the Iranian 2015 nuclear agreement, which was abandoned by former US President Donald Trump but which Iran wants reinstated to allow it to resume key exports of oil.
A senior official in the region, who was briefed by Iranian authorities on Taeb's visit, said that Taeb met several Iraqi militia leaders during the trip and conveyed "the supreme leader's message to them about keeping up pressure on US forces in Iraq until they leave the region".
Since the US air strikes, attacks on US troops and personnel or bases where they operate have intensified in Iraq and widened to eastern Syria.
Iran's foreign ministry did not immediately respond to questions from Reuters for this article, and officials at the Revolutionary Guards public relations office were not immediately available for comment.
Iran's UN envoy this month denied US accusations that Tehran supported attacks on US forces in Iraq and Syria, and condemned US airstrikes on Iranian-backed militants there.
There was no immediate response from the Iraqi government or the prime minister's office to questions about the meeting.
The sources to whom Reuters spoke did so on condition of anonymity due to the sensitivity of the subject.