TEHRAN - Iran's Revolutionary Guards have so many missiles they don't know where to hide them, a senior commander said at Friday prayers, after the United States threatened to impose fresh sanctions.

"We lack enough space in our stockpiles to house our missiles," said General Hossein Salami, the Guards' deputy, as a row with the US over Iran's ballistic missile programme deepened.

"Hundreds of long tunnels are full of missiles ready to fly to protect your integrity, independence and freedom," he told worshippers in Tehran, promising to never "stop developing our defence deterrent".

Iranian state television aired in October unprecedented footage of such an underground missile base.

The general's comments came after reports that the US had planned - but later shelved - to unveil a fresh round of sanctions following two recent missile tests by the Islamic republic.

The mooted financial penalties on companies and individuals in Iran, Hong Kong and the United Arab Emirates, for apparent links to Tehran's missile programme, highlighted worsening US-Iran relations.

They also put in jeopardy a landmark deal struck in July between Iran and six world powers including the US, which is due to be formally implemented within weeks.

Iran's President Hassan Rouhani denounced the US moves Thursday as "hostile and illegal interventions" that must be met with a response.

He ordered the military to intensify its missile development and take whatever steps necessary to start new programmes if they would better serve Iran's defence.

After Rouhani's comments the White House put the sanctions on hold indefinitely, The Wall Street Journal reported, though officials said the measures remained on the table for use if necessary. The spectre of new penalties against Iran - the nuclear deal is due to lift existing sanctions that froze Iran out of the global financial system and crippled its oil exports - brought worsening relations to a head.

A United Nations panel last month said the two missile tests breached previous resolutions aimed at stopping the Islamic republic from developing projectiles capable of carrying a nuclear warhead.

Iran has always denied seeking an atomic weapon and argues that its missiles would never be designed to, nor ever carry, such a bomb.

The nuclear deal is due to come into effect on "Implementation Day", expected later this month, or soon after, when UN monitors sign off that Iran has applied major curbs to its atomic programme.

The Wall Street Journal, quoting unnamed US officials, said that financial sanctions being developed by the US Treasury Department remain on the table, after the decision to delay them.

At one point they were scheduled to be announced Wednesday in Washington, the newspaper said, citing a notification the White House sent to Congress.

The officials gave no definitive timeline for when the sanctions would be imposed, it said.

The WSJ reported Wednesday that the US was preparing fresh sanctions against companies and individuals in Iran, Hong Kong and the United Arab Emirates over alleged links to Tehran's ballistic missile program.

Such a step by the Treasury Department could present a major barrier to the nuclear deal's implementation, let alone its durability, and come with relations between Tehran and Washington deteriorating once more.

They would be the first American sanctions against Iran since Tehran signed the nuclear deal with world powers in July that will eventually see Washington drop separate sanctions targeting that program.

A senior administration official said in a statement to AFP that "we've been looking for some time at options for additional actions related to Iran's ballistic missile program.

"We are considering various aspects related to additional designations, as well as evolving diplomatic work that is consistent with our national security interests."

Earlier Thursday, Iran's President Hassan Rouhani denounced the possible new US penalties, calling them "hostile and illegal interventions" that justified a response.

In the five months since the nuclear deal curtailing Tehran's nuclear ambitions was struck, US officials say Iran has conducted two ballistic missile tests, one of which state media reported at the time, on October 11.