U.S. media reports say the Trump administration escalated a pressure campaign against Iran on Monday by designating the country’s Islamic Revolutionary Guard Corps as a foreign terrorist organization.

It is the first time that an element of a foreign state has been officially named a terrorist entity.

Administration officials said the move is a response to Iran's destabilizing behavior across the Middle East, including support for the regime in Syria, Houthi rebels in Yemen and Hezbollah in Lebanon, as well as for assassination plots in Europe and the US.

Beyond the internal dissent the designation triggered within the US government, the move could also increase tensions with allies, particularly Iraq, where the IRGC has ties to militias and officials, and Lebanon, where it backs Hezbollah, which is part of the government, according to CNN.

Iran's Supreme National Security Council responded Monday by declaring the US a "state sponsor of terrorism" and American troops operating in the region as "terrorist groups," according to IRNA, Iran's state-run news agency.

IRNA says that Iranian Foreign Minister Mohammad Javad Zarif stressed that Iran will not let Washington go unpunished if it dares to designate the Islamic Revolution Guards Corps (IRGC) as a terrorist organization, and warned that Tehran will be prepared for a tough reciprocal response.

"During the session, the Foreign Minister condemned the US possible blacklisting of the IRGC as terrorist group and said such a measure entails numerous dangers," Rapporteur of the Iranian parliament's National Security and Foreign Policy Commission Ali Najafi Khoshroudi quoted Zarif as saying in his Monday meeting with members of the Commission in Tehran.

IRGC Commander Major General Mohammad Ali Jafari warned on Sunday that the US Army will lose its current status of ease and serenity in West Asia if Washington designated the IRGC as a terrorist organization, according to IRNA. 

The Islamic Revolutionary Guard Corps (IRGC) is a branch of Iran's Armed Forces founded after 1979 Revolution on April 22, 1979 by order of Ayatollah Khomeini.  Whereas the regular military (or Artesh) defends Iran's borders and maintains internal order, according to the Iranian constitution, the Revolutionary Guard (pasdaran) is intended to protect the country's Islamic Republic system.  

According to some sources, the Revolutionary Guards have roughly 125,000 military personnel including ground, aerospace and naval forces.