UN sanctions on arms trade and missile sales that are related to nuclear activity will remain in place in any Iran deal, a US official said Tuesday.

"There will be an ongoing restriction on arms just like there will be ongoing restrictions regarding missiles," the senior administration official said.

But the official refused to be drawn on specifics and couched their words carefully, suggesting there could be amendments to existing UN Security Council resolutions.

An Iranian official revealed Monday that Tehran was pushing for removal of any mention of a UN arms embargo in any final nuclear agreement.

"There is no evidence that the arms embargo has any relation with the nuclear issue," the official said.

The US official acknowledged the Iran nuclear talks were "not a missile negotiation, and that "countries are allowed to have a conventional missile programme."

But under UN Security Council resolutions there are "provisions... that are address both technology and missiles capable of carrying nuclear weapons as part of the nuclear-related bases of those resolutions. And that is what we are addressing," the official said.

Negotiators were drafting a new resolution which will go before the UN Security Council to endorse the Iran nuclear deal.

"What this means there will be continued restrictions in this area and we've always said that," the official said.

Since 2006, the UN Security Council has passed six resolutions critical of Iran for its controversial nuclear drive, designed to increase pressure on Tehran to suspend its uranium enrichment and ballistic missiles development programmes.

Resolution 1929 adopted in 2010 after revelations that Iran had built a secret nuclear facility at Qom required UN member states to prevent the transfer of missile-related technology to Iran.

It also banned the sales of such things as tanks, armoured vehicles, attack helicopters and warships to the Islamic republic.

Lavrov says arms embargo 'major problem' in Iran talks
Vienna, Austria (AFP) July 7, 2015 - The lifting of a conventional arms embargo on Iran is a "major problem" in talks between Tehran and world powers towards a nuclear deal, Russian Foreign Minister Sergei Lavrov told Interfax on Tuesday.

"I can assure you that there remains one major problem that's related to sanctions: this is the problem of an arms embargo," Lavrov said after negotiations were effectively extended until Friday.

This view was echoed by a spokesman for the Iranian delegation during the talks in Vienna between Iran and the P5+1 powers -- the United States, Russia, China, Britain, France and Germany.

"The arms embargo is one of the major unresolved issues," the spokesman told AFP.

Tehran wants international restrictions on arms deliveries to Iran to be lifted as part of a deal with world powers curbing its nuclear programme in exchange for sanctions relief.

But a US fact sheet issued after Iran and the six powers agreed a framework nuclear deal in April indicated that these restrictions would remain in place.

Although all UN Security Council resolutions would be lifted, they would be replaced by one new one extending "important restrictions on conventional arms and ballistic missiles," the fact sheet said.

Western officials are uneasy about allowing Iran to buy conventional weapons when it is accused of fomenting unrest in the Middle East, even though it is also fighting Islamic State militants, a common enemy for Washington and Tehran.