The United States has intercepted an order from an Iranian official ordering militants in Iraq to attack American interests in Baghdad such as the U.S. embassy, if the U.S. launches a military strike on Syria, the Wall Street Journal reported, citing intelligence officials.

According to the Journal, the message came from the head of the Revolutionary Guards' Qods Force, which has instructed Shi'ite militia groups in Iraq to be prepared to retaliate against the U.S. with force, in case of a military strike on Syria.

Official believe that the U.S. embassy in Baghdad could be a target, however, they did not elaborate on the likely targets, the newspaper said. Following the threats, the state department issued a travel warning on Thursday, asking U.S. citizens to avoid all unessential travel to Iraq.

"Travel within Iraq remains dangerous given the security situation," the state department said, in its advisory. "Terrorist activity and sectarian violence persist in many areas of the country (Iraq) at levels unseen since 2008," the statement said, adding that “the ability of the embassy to respond to situations in which U.S. citizens face difficulty, including arrests, is extremely limited."

President Barack Obama has sought congressional approval for his plan to strike Syria in a limited assault to punish Bashar Assad's government for using chemical weapons against the country's citizens. And, various militant groups in Iran and Iraq are reportedly plotting revenge against the U.S. and Israel, if the former attacks Syria.

“If there are strikes, there’s going to be an intense debate inside Iran as to whether or not respond, and if so how,” Trita Parsi, who heads the National Iranian American Council, told the Washington Post. “I think it’s quite clear that the more moderate elements are not particularly inclined to get involved in a direct confrontation with the U.S.”

Iran’s Supreme Leader Ayatollah Ali Khamenei and top officials in the nation’s military have said that any U.S. strike will lead to attacks on U.S. interests in the Middle East, the Washington post reported.