Iran has rejected suggestions it is willing to discuss its missile programme with the US.
A spokesman for Iran's UN Mission said the weapons "are absolutely and under no condition negotiable".
His denial comes after Foreign Minister Mohammad Javad Zarif suggested in an interview the missiles could be up for discussion if sanctions are lifted.
The US unilaterally withdrew from a landmark 2015 nuclear deal last year and reimposed tight restrictions.
In response, Iran announced in July it has surpassed limits on enriched uranium imposed in the agreement. The country insists it is not trying to build nuclear weapons.
What did Iran say?
In a television interview on Monday, Mr Zarif told broadcaster NBC News that "room for negotiation is wide open" once the US removed its punishing sanctions.
Asked if this would include discussions about Iran's missiles - something absent from the original 2015 agreement - Iran's foreign minister said if the US wanted to discuss the programme "they need, first, to stop selling all these weapons, including missiles, to our region".
But Alireza Miryousefi, a spokesman for Iran's UN Mission, said Iran "categorically rejects" the "characterization" of their foreign minister's interview, and attacked media reports of his words.
"Drawing a false conclusion in pursuit of headlines, when what was said in the context was obvious, only leads to a diminution of the standing of the press with the public," he tweeted.
At a cabinet meeting on Tuesday, US Secretary of State Mike Pompeo said Iran had "for the first time" shown its willingness to discuss the weaponry. The country has previously insisted this was not an option under any circumstances.
President Donald Trump said the US had made "a lot of progress" with Iran and that they were "not looking for regime change", although he insisted the country cannot develop a nuclear weapon and "can't be testing ballistic missiles".
Meanwhile the president's nominee for defence secretary, Mark Esper, told the Senate Armed Services Committee on Tuesday the US is not looking for war with Iran and needs to "get back on the diplomatic channel".
Is the nuclear deal still in effect?
President Trump withdrew the US from the nuclear deal in May 2018. He argued it did not go far enough to curb their nuclear programme, and said he wanted to replace it with a new agreement that would also limit the country's missile programme.
Iran has refused to negotiate any changes, and has threatened to further break the terms of the agreement if Europe does not help limit the effects of US sanctions.
EU foreign ministers on Monday urged Iran to "go back to full compliance", arguing the recent breaches have not been significant and are all "reversible".
Israeli Prime Minister Benjamin Netanyahu has criticised Europe's response, saying it would not understand the threat "until Iranian nuclear missiles fall on European soil".
What about tensions in the Gulf?
The US has sent warships to the Gulf amid the heightened tensions over the deal, and also over attacks on six oil tankers passing through the area in May and June.
Iran has denied US allegations it was behind the attacks.
The UK has also sent warships to the area after detaining an Iranian tanker in Gibraltar under suspicion it was carrying fuel to Syria.
Iran denied it was en route to Syria and threatened to seize a UK tanker in response.
On Tuesday, a US defence official said a small oil tanker belonging to the UAE - the Riah - could have been taken by Iran's Revolutionary Guards. It stopped transmitting its position days ago as it sailed through the Gulf.
Semi-official Iranian news agency ISNA then reported forces from the country had come to the tanker's aid "after receiving a request for assistance".