In a show of defiance to the West, Iran announced on Tuesday the opening of a new underground depot for its Emad precision-guided missiles that can be fitted with nuclear warheads.

Iran's state television said the underground facility is situated in mountains and run by Iran's Revolutionary Guards, Reuters reported. The underground missile depot was inaugurated by the speaker of parliament, Ali Larijani.

It was the second such underground facility for missiles shown by Iran, with the first one also publicised last October.

The Revolutionary Guards' second-in-command, Brigadier General Hossein Salami, boasted last Friday that Iran's depots and underground facilities are now so full of missiles that they're having problems on how to put all their new weapons inside the facility.

The underground facility was intended as an umbrella to protect Iran's missiles and other military assets from possible enemy airstrikes, sources say.

The Pentagon says the Emad, which Iran tested in October, would be capable of carrying a nuclear warhead. Iran would be in violation of a 2010 U.N. Security Council resolution once placement of a nuclear warhead on the missile is verified.

U.S. officials say Washington will respond to the Emad missile tests with fresh sanctions against Iranian individuals and businesses linked to the programme.

The fact that Iran is openly showing to the world its missile capabilities poses a challenge for the United States and European Union, which are about to remove nearly all international sanctions against Tehran under the nuclear deal reached last July.

Iran has complied with the basic terms of the nuclear deal, which require it to give up material that world powers feared could be used to make an atomic weapon and accept other restrictions on its nuclear programme.

At the same time, however, Iranian President Hassan Rouhani ordered his defence minister last week to expand the country's missile programme.

Experts say the new Iranian missiles are much more effective than previous ones since the Iranians have managed to improve the missiles' accuracy.