By Laura Trevelyan
BBC News, New York
Negotiations at the United Nations over a resolution imposing further sanctions over Iran have been paused briefly.
Iran insists its nuclear programme is entirely civilian
Britain, France and the US want a vote on Saturday but Qatar, Indonesia and South Africa, members of the Security Council, have concerns.
President Ahmadinejad of Iran has been given a visa by the US government so he can be present for the vote.
The five permanent members of the security council and Germany proposed new sanctions against Iran last week.
These include a ban on the export of arms from the country and freezing the financial assets of key individuals and institutions involved in Iran's nuclear programme.
Ban on Iranian arms exports
Call for end to new loans
Travel restrictions on people involved in Iran's programme
Freeze on the assets of key Iranian leaders
Iran given 60 days to halt enrichment or face further measures
But there are three members of the Security Council with objections.
Qatar and Indonesia want the resolution to call for a nuclear-free Middle East - meaning Israel should get rid of its nuclear weapons.
Russia has suggested some compromise language.
South Africa has called for major changes, most of which have been rejected.
However, diplomats say the idea of Russia enriching uranium for Iran has been included, an notion approved by South Africa.
The five permanent members of the Security Council would like this resolution to be passed unanimously.
This would send a stronger signal to Iran than if there is a divided Council.
The full Council meets again later on Friday with the possibility of a vote on Saturday.
The detention of the 15 British servicemen by Iran will only heighten the tension - the French ambassador described this as a "concerning development".