Iran has promised a "crushing" response if the US designates the nation's Islamic Revolution of Guards Corps (IRGC) as a terrorist group. The elite army's chief has also threatened Washington that Iran will consider the US military as Islamic State (Isis).

The threat comes days before US President Donald Trump is set to outline his broader policies pertaining to Iran, during which he is widely expected to label the powerful IRGC as a terrorist organisation. The American leader is also expected take a final call on how to deal with the nuclear accord that global powers had signed with Iran in 2016.

"If the news is correct about the stupidity of the American government in considering the Guards a terrorist group, then the Guards will consider the American army to be like Daesh [Arabic name for Islamic State] all around the world, particularly in the Middle East," said IRGC chief Mohammad Ali Jafari.

"As we've announced in the past, if the US' new law for sanctions is enforced, the country will have to move their regional bases outside the 2,000km range of Iran's missiles. We will use any silly behaviour by the Trump administration as an opportunity to advance our defensive and missile program," added the top Iranian military general.

Multiple power centres in Iran have issued a warning to the US to not take any extreme steps while dealing with Iran. Though multiple individuals and entities linked to IRGC are already on the US' list of terrorist groups, the IRGC – Iran's most powerful security force – is not on the list as a group.

"We are hopeful that the United States does not make this strategic mistake," said Iran's foreign ministry spokesperson Bahram Qasemi, reported the IRNA news agency. "If they do, Iran's reaction would be firm, decisive and crushing and the United States should bear all the consequences."

Iran's foreign minister Mohammad Javad Zarif also issued a similar warning not to label the IRGC as a terrorist group but did not specify how Tehran would react.