South Africa, a member of the 35-nation IAEA board, has played a key role in efforts to ensure a deal on Iran in line with its policy of giving all nations the right to use nuclear energy for civilian purposes.
Tehran says it wants nuclear power only for electricity but the IAEA, the UN nuclear watchdog, is likely to report Iran to the Security Council over fears that it may be using its nuclear programme to build atom bombs.
The IAEA vote, originally due late on Friday has been deferred to Saturday.
Should it be reported to the Council, Iran has threatened to respond by stopping UN spot checks of its atomic sites as part of the world treaty to deter clandestine nuclear bomb-making.
Russia and China have endorsed a European-sponsored resolution to put the council on notice as long as Tehran is given at least a month to co-operate fully with the UN investigations before further action, possibly sanctions, are taken.
Aziz Pahad, the South African deputy foreign minister and main diplomat for the Middle East, said that whatever decision is taken, it would not aggravate the situation and that there would still be room for negotiation.