Iran has delivered its formal response to the demand by world powers that it suspend uranium enrichment in exchange for a package of incentives.
Iran says its nuclear programme is for power generation only
Iranian TV said the response was handed over in Tehran to diplomats from the five permanent UN Security Council members plus Germany.
The details were not immediately released, but Iran made clear on Monday that it would reject global pressure.
Supreme leader Ali Khamenei said Tehran would pursue its nuclear activities.
Iran's top nuclear negotiator Ali Larijani has now handed a written response to the envoys representing the US, UK, Russia, China, France and Germany, Iranian television reported.
The US, which broke off diplomatic relations with Iran during the Islamic revolution in 1979, is represented by the Swiss in the Iranian capital.
US ambassador to the United Nations John Bolton described Iran's response as a significant moment:
"We will obviously study the Iranian response carefully, but we are also prepared if it does not meet the terms set by the permanent five foreign ministers to proceed here in the Security Council, as the ministers have agreed, with economic sanctions.
"If on the other hand the Iranians have chosen the path of co-operation, as we've said repeatedly then a different relationship with the United States and the rest of the world is now possible."
The incentives on offer include help with civilian nuclear technology.
The package was devised amid fears that Iran is trying to develop a nuclear weapons programme - a claim that Iran denies.
The UN Security Council has demanded Iran suspend uranium enrichment by 31 August or face the threat of unspecified economic and diplomatic sanctions.
Ayatollah Khamenei said Iran would "continue its path"
Ahead of its release, Iranian officials said the formal response would be "multi-faceted" - not just "yes" or "no" - and address ambiguities over its right to nuclear technology.
Iran has already said it would like further negotiations to resolve the nuclear dispute, says the BBC's Mike Sergeant at the UN headquarters in New York.
Tuesday was a self-imposed deadline for Iran to respond to the incentives proposed on 6 June by the six nations.
It had said it would respond by the end of the Iranian month of Mordad - which finishes on Tuesday.
As well as help with a civilian power programme, the suggested package offers Iran a partial lifting of economic sanctions.
Enriched uranium is used as fuel for nuclear reactors, but highly enriched uranium can also be used to make nuclear bombs.
Iran maintains that its nuclear programme is for civilian use only. It points out that as a signatory to the nuclear non-proliferation treaty (NPT) it is entitled to a nuclear power programme and says it has broken no rule.
But the Western powers accuse Iran of concealing an enrichment programme, and Washington has refused to rule out military action.