Diplomats said China, Europe, Russia and the United States were closing ranks behind a resolution sending Tehran to the UN over fears it may be secretly developing an atomic bomb.
However some non-aligned countries threw a spanner in the works by demanding that the resolution also include mention of a Middle East nuclear-weapons-free zone, diplomats said.
Tehran is threatening to start industrial scale uranium enrichment if the matter is sent to the UN Security Council, which has the power to impose sanctions.
The non-aligned diplomats want the zone to be mentioned if Iran is to be reported to the Security Council but the United States is opposed to the plan, diplomats said.
Washington fears that if the nuclear weapons-free zone is mentioned in the resolution, "it will stay there forever and allow the Iranians to hide behind it," avoiding IAEA demands, a diplomat said.
Egypt, however, is lobbying strongly for the zone to be mentioned in the resolution, diplomats said.
Egypt and other Arab states regularly insist that Israel, which is believed to have nuclear weapons, be part of a general security framework in the Middle East that bans atomic weapons.
Despite the complication, diplomats said the major powers were closing ranks behind a decision to send Tehran to the Security Council.
"We're in a consultation phase right now," said a Western diplomat who asked not to be named, expressing confidence that non-aligned concerns would be met without affecting the referral of Iran to the Security Council.
US Ambassador Gregory Schulte told reporters the West was convinced "that we have a solid majority in support of the resolution that reports Iran to the Security Council and that majority is growing."