Major powers need more talks on Iran's nuclear programme before a further UN resolution can be tabled, the US says.
A US state department spokesman said some issues remained unresolved, but that "all parties remain committed to a second resolution in the near future".
The US, UK, France, Russia, Germany and China held telephone talks on Saturday, which their UN envoys will now take up.
The UN nuclear watchdog confirmed last month that Iran had ignored a deadline to suspend its nuclear activities.
Tehran insists it has a right to a peaceful nuclear programme and has refused to halt uranium enrichment.
'Positive atmosphere'
Following Saturday's telephone conference, US state department spokesman Kurtis Cooper said some work remained to be done "on a few outstanding issues".
Political directors from the six countries involved had "had a good discussion in keeping with the positive atmosphere of their conversations last week", he said in a statement.
The latest telephone conference followed similar talks on Thursday and a meeting on Monday in London.
US officials have expressed hopes that UN ambassadors from the six powers could begin drafting a resolution next week.
New tougher sanctions could include travel bans on Iranian officials associated with nuclear and missile programmes.
Claims denied
Iranian President Mahmoud Ahmadinejad has said his country will not go back on its nuclear programme.
He held talks with Saudi Arabia's King Abdullah on Saturday that were expected to touch on the issue, as well as sectarian violence and regional tensions.
Iran denies Western claims it is secretly trying to build nuclear arms, saying its nuclear programme is for peaceful, energy-producing purposes.
The UN Security Council imposed sanctions on Iran in December, setting a 60-day deadline for it to stop enriching uranium.
But a report last week by the International Atomic Energy Agency (IAEA) said that Iran was instead expanding the programme.
Enriched uranium is used as fuel for nuclear reactors, but highly enriched uranium can be used to make nuclear bombs.
(BBC News, 04/03/2007)