The US has rejected a call from the head of the UN's nuclear watchdog for a "timeout" in the showdown with Iran over its nuclear programme.
Iran has refused to halt enrichment of uranium
The US ambassador to the UN said the sanctions already being applied against Iran were not open to reinterpretation.
The head of the IAEA, Mohamed ElBaradei, said on Friday that Iran's nuclear work and UN sanctions could be simultaneously stopped.
Some Western nations fear Iran is trying to build nuclear weapons.
Tehran insists its programme is for peaceful uses only.
A UN resolution passed on 23 December imposed sanctions on Iran until it stops enriching uranium.
Enriched uranium is used as fuel for nuclear reactors but can also be used to produce material for atomic weapons.
The acting US ambassador to the UN, Alejandro Wolff, said "there is a path laid out for suspension [of sanctions] and that is Iranian suspension of their enrichment activities to be responded to by the Council."
UN SANCTIONS ON IRAN
Ban on import and export of nuclear-related material
Assets frozen of 10 companies and 12 individuals
Threat of further non-military sanctions
Iran too has dismissed the proposal. Chief nuclear negotiator Ali Larijani said Mr ElBaradei's proposal was not "mature" enough.
"Iran's nuclear issue has different angles and sides to it, and does not have a simple one-line solution," he said in Tehran.
Iran has been pressing ahead with plans to expand its nuclear programme.
Tehran has announced it will install 3,000 centrifuges at its Natanz nuclear facility. This would be a massive increase in its potential to produce enriched uranium.
On Friday Iran demanded the removal of the UN official in charge of inspecting the country's nuclear programme.
The official, Chris Charlier, had already been banned from entering Iran.
Last week, Iran banned 38 inspectors from four different countries.