American intelligence authorities say they have captured Iranian instructions to militants in Iraq to strike US interests in Iraq if Syria was attacked.
The Wall Street Journal reported that Baghdad was the target but intelligence officials did not go into detail about what the targets could be.
The message was alleged to have come from the head of the Revolutionary Guards' Qods Force to Shia militant groups in Iraq.
The State Department issued a warning on Thursday warning US citizens against all non-essential travel to Iraq.
US officials also worry that Iran's proxy group in Lebanon, Hezbollah, could attack the embassy in Beirut.
On Friday, the State Department ordered all of its 'non-essential' diplomats out of Lebanon amid growing fears of a strike.
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As Congress begins to debate airstrikes on Syria, US forces are mounting in the eastern Mediterranean and the Red Sea including an aircraft carrier and numerous destroyers.
The US has also readied Marines to evacuate diplomatic compounds.
As tension mounts over a US strike, Iran has increased its rhetoric in support of Syria's regime.
Forghani said that within 21 hours, “...a family member of every U.S. minister [department secretary], U.S. ambassadors, U.S. military commanders around the world will be abducted. And then 18 hours later, videos of their amputation will be spread [around the world].”
Last week, Iran’s Revolutionary Guards chief said that a US military attack on Syria would lead to the “imminent destruction” of Israel and would become a “second Vietnam” for America.