Mrs Clinton accused Iran to trying to deflect pressure on the nuclear issue
Plans for a fourth set of UN sanctions against Iran over its nuclear programme are being circulated among all 15 members of the Security Council.
US Secretary of State Hillary Clinton said the five veto-wielding members had agreed on a "strong" draft resolution.
The measures foresee cargo ship inspections and new banking controls.
They come despite a recent deal in which Iran agreed to send low-enriched uranium to Turkey in return for enriched fuel for a research reactor.
But Mrs Clinton suggested Iran had been trying to deflect pressure.
Jon Leyne, BBC Tehran correspondent
This is Washington's answer to what was widely seen as a last-minute attempt by Iran to head off new sanctions.
Indeed, in slightly triumphant tone, Hillary Clinton said it was as convincing an answer as it was possible to provide.
It appears that the two more sceptical big powers, Russia and China, have not been convinced by Iran's agreement to ship out a large part of its stocks of enriched uranium to Turkey.
For US officials the core issue was that Iran intended to continue enriching uranium, which the UN has banned, the BBC's Barbara Plett reports from New York
The Turkish deal, which Brazil helped to negotiate on Monday, was similar to one proposed by the West and its allies last year.
The members of the Security Council, which includes Turkey and Brazil, were holding a session behind closed doors on the resolution, but Brazil reportedly said it would not discuss the draft "at this point".
The US is quite confident of getting a majority of Council members behind the resolution although it may not get unanimity, our correspondent says. The vote is expected in June.
The sanctions, she adds, are not as strong as Western states would have wanted and some proposals were watered down by Russia and China.
China's UN Ambassador Li Baodong said on Tuesday that "the purpose of sanctions is to bring the Iranian said to the negotiating table".
"The sanctions are not for punishing innocent and should not harm normal trade," he added.
Russia's UN Ambassador Vitaly Churkin described the draft resolution as "well balanced".
"That's why we agreed to accept the text on the whole after the long discussions and corrections of the initial proposals and we find it to be an appropriate one," Mr Churkin was quoted as saying by Russia's Itar-Tass news agency.
There have been three rounds of UN sanctions against Iran, blocking trade of "sensitive nuclear material", freezing the financial assets of those involved in Iran's nuclear activities, banning all of Iran's arms exports and encouraging scrutiny of the dealings of Iranian banks.
The US and its Western allies fear that Iran is secretly trying to build a nuclear bomb. Tehran says its programme is aimed solely at peaceful energy use.
Proposals in the 10-page resolution include:
• A comprehensive new framework for cargo ship inspections both in ports and on the high seas if there is reason to suspect a ship is carrying conventional arms or nuclear missile items
• A ban on countries selling tanks, armoured combat vehicles, warplanes, warships and other heavy weapons to Iran
• A ban on the opening of new branches, subsidiaries or representative offices of Iranian banks if there are grounds for believing that they are linked to nuclear proliferation
• Greater vigilance over transactions involving Iranian banks in order to prevent such transactions contributing to proliferation of sensitive nuclear activities
• The placing of more members of the Revolutionary Guards on a list to have their assets frozen
Brazil's UN envoy said his country was not "engaging in any discussion on a draft at this point because we feel that there is a new situation".
"There was an agreement yesterday which is a very important one," Maria Luiza Ribeiro Viotti was quoted as telling reporters on the sidelines of the Security Council meeting.
Earlier, Turkish Prime Minister Recep Tayyip Erdogan called on the world to support Monday's deal with Iran.
But he added that if Iran did not ship out the uranium within one month, as agreed, then it would be on its own.
Mrs Clinton addressed the US Senate foreign relations committee after talks between the five permanent Security Council members - the US, UK, Russia, China and France - and Germany.
"We have reached agreement on a strong draft with the co-operation of Russia and China," she said.
Mrs Clinton said she had spent Tuesday morning on the phone with her Russian counterpart, Sergei Lavrov, "finalising the resolution".
Russia and China have previously resisted calls for a new round of sanctions.
Talking about the Turkish deal, Mrs Clinton accused Tehran of trying to deflect pressure from the major powers.
"We don't believe it was any accident that Iran agreed to this declaration as we were preparing to move forward in New York," she said.
"The fact that we had Russia on board, we had China on board and that we were moving early this week, namely today, to share the text of that resolution, put pressure on Iran which they were trying to somehow dissipate."