Iran’s most prominent military leader has recently met Iraqi militias in Baghdad and told them to “prepare for proxy war”, the Guardian has learned.

Two senior intelligence sources said that Qassem Suleimani, leader of Iran’s powerful Quds force, summoned the militias under Tehran’s influence three weeks ago, amid a heightened state of tension in the region. The move to mobilise Iran’s regional allies is understood to have triggered fears in the US that Washington’s interests in the Middle East are facing a pressing threat. The UK raised its threat levels for British troops in Iraq on Thursday.

While Suleimani has met regularly with leaders of Iraq’s myriad Shia groups over the past five years, the nature and tone of this gathering was different. “It wasn’t quite a call to arms, but it wasn’t far off,” one source said.