Iran promised on Monday to give a "crushing" response if the United States designated its elite Revolutionary Guards as a terrorist group.
The pledge came a week before President Donald Trump announces a final decision on how he wants to contain Tehran. He is expected on Oct 15 to decertify a landmark 2015 international deal to curb Iran's nuclear program, in a step that potentially could cause the accord to unravel.
Trump is also expected to designate Iran's most powerful security force, the Revolutionary Guards Corp (IRGC) as a terrorist organization, as he rolls out a broader U.S. strategy on Iran.
"We are hopeful that the United States does not make this strategic mistake," foreign ministry spokesman Bahram Qasemi was quoted as saying by the state news agency IRNA at a news conference.
"If they do, Iran's reaction would be firm, decisive and crushing and the United States should bear all its consequences," he added.
Individuals and entities associated with the IRGC are already on the U.S. list of foreign terrorist organizations, but the organization as a whole is not.
IRGC commander Mohammad Ali Jafari said on Sunday "if the news is correct about the stupidity of the American government in considering the Revolutionary Guards a terrorist group, then the Revolutionary Guards will consider the American army to be like Islamic State all around the world."
Jafari also said that additional sanctions would end the chances for future dialogue with the United States and that the Americans would have to move their regional bases outside the 2,000 km (1,250 mile) range of IRGC's missiles.