Iran said on Friday it would retaliate against any action targeting its armed forces and accused the United States of violating the spirit of the 2015 nuclear deal reached between Tehran and six major powers.

US President Donald Trump is expected later on Friday to take a major step against the nuclear deal, laying out a more aggressive approach to Iranian activities in the Middle East that risks upsetting US ties with European allies.

"Iran will strongly respond to any action against its military forces, including the Revolutionary Guards Corps," Foreign Ministry spokesman Bahram Qasemi was quoted as saying by state TV. A senior US official, speaking on condition of anonymity, said on Friday that steps Trump is reviewing as part of a broader strategy also include imposing targeted sanctions in response to Iran's ballistic missile tests, cyber espionage and backing of Lebanese Hezbollah and other groups on the U.S. list of foreign terrorist organisations.

The US administration earlier this year considered, but then put on hold, adding the Islamic Revolutionary Guard Corps, Iran's most powerful internal and external security force, to the U.S. list.

Qasemi said Iran will continue building up its ballistic missile capability in defiance of Western criticism, with Washington saying the Islamic Republic’s stance violates the nuclear deal with the powers.

"Iran's missile programme is only for defensive purposes... we are determined and serious about expanding it," he said.

Qasemi also warned about possibility of pulling out of the deal. "Iran always acts based on its interests and will continue to do so. If necessary, we can also withdraw from the deal," Qasemi said.