"It’s been too long we have been debating … we have to pass the sanction resolution" at the UN Security Council, US undersecretary of state for political affairs Nicholas Burns said to journalists on the margins of a conference of the pan-European OSCE watchdog.
"It is not that complicated," he added, "we need to send a strong message to the Iranians". The six world powers are to meet Tuesday in Paris in their latest bid to secure agreement on a package of sanctions against Iran for its refusal to suspend sensitive nuclear activities.
High-ranking diplomats from the five veto-wielding UN Security Council members plus Germany will attend the talks at the French foreign ministry.
A representative of European Union policy chief Javier Solana will also take part in the meeting.
Burns said that the participants would "see if we can narrow our differences and agree so that our ambassadors (at the UN) in New York should pass in the quickest possible time a decisive sanction resolution".
World powers have been trying for weeks to agree what sanctions to impose on Iran for its refusal to comply with a UN deadline to freeze uranium enrichment, which can be used to generate electricity or to build atomic weapons.
A draft resolution circulated by Britain, France and Germany would have barred trade with Iran in goods related to its nuclear and ballistic missile programmes and applied financial and travel restrictions to persons and agencies involved in either area.
But Russia and to a lesser extent China, have tried to water down the text, saying the sanctions should not target individuals and should be limited in duration.
Meanwhile Washington wants to harden at least the wording of the text.