President Donald Trump's administration on Monday urged U.S. diplomats abroad to push allies to designate Iran's Islamic Revolutionary Guard Corps and Lebanon-based Hezbollah as terrorist groups, citing elevated risk of attack, according to an internal State Department cable seen by Reuters.

The directive, dated Monday and signed by  Secretary of State Marco Rubio, was sent to all U.S. diplomatic and consular posts worldwide.

It asks U.S. diplomats to deliver the message to their counterparts "at the highest appropriate level" and no later than Friday, adding that the advocacy efforts to get these groups blacklisted should be coordinated with Israeli counterparts.

The Trump administration is attempting to rally reluctant allies - many of whom were not briefed ahead of the U.S.-Israeli air war that started two weeks ago - to support its military operation.

In one sign of trouble for that effort, several U.S. allies said on Monday they had no immediate plans to send ships to help the U.S. unblock the Strait of Hormuz, rebuffing Trump's plea to keep the vital oil shipping waterway open.

"With the elevated risk of attack from Iran and its partners and proxies, all governments must move expeditiously to diminish the capabilities of Iran and Iran-aligned terrorist groups from attacking our respective nations and citizens," one of the talking points in the cable said.

The IRGC is an elite military force whose purpose is to protect Shi'ite Muslim clerical rule in Iran. It controls large parts of Iran's economy. Both the IRGC and the Lebanon-based Shi'ite Muslim armed group Hezbollah are already designated as terrorist groups by the United States and some other countries.

The cable does not provide details on the elevated risk but cites examples of how Tehran has attacked its neighbors in the Middle East and urges joint action.

"We assess that the Iranian regime is more sensitive to collective action than unilateral action, and that joint pressure is more likely to compel behavior change by the regime than unilateral actions alone," the cable said.

It adds that such designations would increase pressure on the Islamic Republic and limit its ability "to sponsor terror activities" around the world.

"President Trump is focused on securing peace in the Middle East," a State Department spokesperson said. "The IRGC, Hezbollah, and other Iranian backed proxies destabilize governments and undermine regional peace."