US declares Iran's Guard a 'terrorist' group

US President Donald Trump on Monday designated Iran's elite Islamic Revolutionary Guard Corps [or IRGC] a "foreign terrorist" organisation, an unprecedented step that raises tension in the Middle East.

Iran's Supreme National Security Council immediately declared the United States a "state sponsor of terrorism" and US forces in the region "terrorist groups," state media said.

In a statement carried by the official news agency IRNA, it said the move was in response to Washington's "illegal and foolish act" of designating Iran's Revolutionary Guard a terrorist organisation.

"No other country has the legal right to designate as terrorist another country's armed forces ... Iran's influence in the Middle East and its success in fighting against Islamic State [Daesh] are reasons behind this designation," state TV said, without quoting a specific official.

Iran Foreign Minister Javad Zarif called for US forces to be put on "Iran's list of terror groups."

It is the first time the US has formally labelled another country's military a terrorist group.

"The IRGC is the Iranian government’s primary means of directing and implementing its global terrorist campaign," Trump said in a statement.

Israel and Bahrain were quick to welcome Trump's announcement. 

The designation "makes crystal clear the risks of conducting business with, or providing support to, the IRGC," Trump said. 

"If you are doing business with the IRGC, you will be bankrolling terrorism."

Critics have warned that the move could open US military and intelligence officials to similar actions by unfriendly governments. 

The United States has already blacklisted dozens of entities and people for affiliations with the IRGC, but not the organisation as a whole.

The IRGC is a paramilitary organisation formed in the wake of Iran's 1979 Islamic Revolution to defend its clerically overseen government. The force answers only to Iran's supreme leader, and operates independently of the regular military. 

Also on Monday, US Secretary of State Mike Pompeo told a news conference the designation will take effect in one week.

The announcement comes shortly before the first anniversary of Trump's decision to pull out of a 2015 nuclear deal with Tehran and to reimpose sanctions that had crippled Iran's economy.

Iran had earlier warned it will take reciprocal action.

"We will answer any action taken against this force with a reciprocal action," a statement issued by 255 out of the 290 Iranian lawmakers said, according to IRNA.

Trita Parsi, the former president of the National Iranian American Council, explains the ramifications of the move.