The surprise suspension of the morning session of the 35-nation board of governors of the International Atomic Energy Agency (IAEA) came as the United States and 14 allies were intensely lobbying other member states to back them in a resolution on Iran's nuclear program.
IAEA spokesman Mark Gwozdecky said no time was yet set to resume the meeting. The board of governors have been meeting here since Monday.
"They are still in negotiations, still in progress. There is no reason to go into a plenary session and then say we've got to leave for more informal talks," a Western diplomat told AFP.
"The bottom line is that we're still working behind the scenes to bring as many people on board for the resolution as possible," he said.
He said the process was slow since national representatives had to check back with their governments, with responses to questions asked after evening talks sometimes not coming back until the following afternoon.
The United States and its co-sponsors are confident they have the votes to get the IAEA to impose a deadline on Iran to fully disclose all details on its nuclear program.
Iran, which denies it is trying to develop nuclear weaons, has reacted strongly against the possibility of a deadline, as well as the draft resolution's call for it to cease its enrichment activities.
In Tehran, Foreign Minister Kamal Kharazi denounced the "arrogance" and "extremist posture" of certain countries over Iran's nuclear program and warned Tehran might reconsider its cooperation with the Vienna-based IAEA.
The Western diplomats said the 15 co-sponsors of the resolution, which also calls on Iran to reveal whether it is enriching uranium to weapons-grade level, felt they had a majority of 20 to 22 nations.
The co-sponsors include the United States, Germany, Britain, France and Japan.
These countries held informal talks Wednesday evening with hold-out IAEA members, particularly Russia and non-aligned countries led by Malaysia which want a softer resolution without a deadline.
The US ambassador to the IAEA, Ken Brill, said: "What the board members are being called on right now to do is to strengthen the hand of the agency as it seeks to pursue its safeguards responsibilities in support of the" nuclear Non-proliferation Treaty (NPT).
Washington claims Tehran is hiding a program to develop atomic weapons. US President George W. Bush has identified Iran as part of an "axis of evil" of countries trying to manufacture weapons of mass destruction that included then Saddam-ruled Iraq and North Korea.
IAEA chief Mohamed ElBaradei had said Wednesday that he thought "there is broad agreement the (IAEA) would like to see a deadline by which Iran should present all the information (on its nuclear activities) we need to have in order to bring this issue to closure."