The U.S. Embassy in Iraq has warned Americans to leave the country as soon as possible over threats from militias aligned with Iran to carry out imminent attacks in Baghdad over the next two days.

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“U.S. citizens should leave Iraq now,” the embassy warned in an alert published Thursday. Anyone who chooses to remain in the country will do so “at significant risk,” it added.

The warning came just days after reports emerged of the kidnapping of American journalist Shelly Kittleson, who was feared to have been abducted in Baghdad on Tuesday by suspected Iranian-backed militants.

Dylan Johnson, the assistant secretary of state for global affairs, said a person believed to have been involved in the kidnapping had been captured and was in Iraqi custody. He said the person had ties to the Iranian-aligned militia Kataib Hezbollah.

Kittleson’s mother, Barb Kittleson, told NBC affiliate WTMJ of Milwaukee that her daughter had been living in the Middle East and working as a journalist for about 20 years. She said she last heard from her Monday.

Since the United States and Israel launched their military assault on Iran in late February, triggering the war currently consuming the region, the U.S. Embassy in Baghdad has been warning that militias within Iraq may try to kidnap Americans.

The embassy on Thursday noted that Iran and Iran-aligned militias have previously carried out “widespread attacks” against U.S. citizens and targets associated with the U.S. in Iraq, including in its semiautonomous Kurdistan region.

While Iraq as a whole became safer for locals and foreigners when the civil war triggered by 2003 U.S. invasion wound down, Iran’s influence over its neighbor’s politics and society has grown. Iranian-backed Popular Mobilization Forces, which are legally part of the Iraqi military, often act independently from the government.

The embassy said that in addition to the risk of kidnapping, “businesses, universities, diplomatic facilities, energy infrastructure, hotels, airports, and other locations perceived to be associated with the United States, as well as Iraqi institutions and civilian targets,” could also be subject to attack.

It added that the Iraqi government has not prevented attacks in or from its territory. It also warned that militia members could even “claim to be associated with the Iraqi government” and may carry identification denoting their status as government employees.

Iraq’s embassies in the U.S. and Britain did not immediately respond to requests for comment from NBC News.

The development comes after the State Department last month ordered all U.S. embassies and consular posts worldwide to conduct security reviews without delay, according to a cable seen by NBC News following attacks on U.S. embassies in the region, including an attack by an Iran-aligned militia on the embassy in Baghdad.

Americans looking to leave Iraq, where a “Level 4: Do Not Travel” warning is in effect, will face some difficulty, with the airspace closed and commercial flights not operating out of the country.

The embassy noted that overland routes to Jordan, Kuwait, Saudi Arabia and Turkey were open, but that travelers should “expect long delays.”

Still, it said, Americans should “depart now via one of these overland routes.”

It further warned Americans not to attempt to travel to the embassy in Baghdad or the consulate general in Irbil “in light of significant security risks,” but said Americans in need of assistance could contact the embassy in Baghdad at BaghdadACS@state.gov or the consulate general in Irbil at ErbilACS@state.gov.

Irbil is the capital of the oil-rich Kurdistan region, which has seen less violence than other parts of the country.

The embassy suggested that Americans leaving the country keep a “low profile” and “stay aware of your surroundings.” It also suggested having a supply of food, water, medications and other essential items.

Meanwhile, the Iraqi Interior Ministry has said it continues to work to “secure the release” of Kittleson, the American journalist kidnapped in Baghdad this week.

It said it would “take all necessary legal measures against all those involved in this criminal act, in accordance with the law.”