Opposition from UN Security Council veto powers China and Russia is expected to block a resolution to extend the blockade beyond October.

Pompeo reiterated during a visit to Vienna that Iran should not be allowed to buy and sell weapons, calling the Islamic Republic "the world's largest state sponsor of terrorism".

"I mean that's just nuts... We're urging the whole world to join us" to extend the arms embargo, he said.

As things stand arms sanctions are set to be eased gradually from October, under a Security Council resolution blessing a 2015 deal Iran signed with world powers to limit its ability to develop a nuclear bomb -- in exchange for easing trade barriers.

The landmark deal has come under strain since the US pulled out of it in 2018.

As Washington has re-imposed crippling sanctions, Tehran has in turn stepped up its nuclear activities again since last year.

Pompeo urged Tehran to provide "full, transparent and immediate cooperation" with the International Atomic Energy Agency (IAEA), which monitors Iran's compliance with the nuclear deal.