* World powers agreed wording of a rebuke to Iran
* UN nuclear agency board was set to vote Thursday
* Amendment creates "procedural chaos" - Western diplomat
By Fredrik Dahl
VIENNA, Sept 13 (Reuters) - South Africa proposed a last-minute change to a U.N. nuclear agency resolution rebuking Iran on Thursday, throwing the meeting into confusion, diplomats said.
Six world powers put forward the draft text on Wednesday, aiming to add diplomatic pressure on Tehran, a day after Israel ramped up threats to attack the Islamic Republic which it believes is seeking nuclear weapons capability.
Intended to signal big power unity and criticise Iran for defying U.N. calls to curb its nuclear work, the full 35-nation governing board of the International Atomic Energy Agency (IAEA) had been expected to vote on and approve the text on Thursday.
But South Africa, like Iran a member of the Non-Aligned Movement (NAM) of mainly developing nations, proposed a change to the board resolution agreed by the United States, Russia, France, China, Britain and Germany.
As a result the board meeting that started at 10 a.m. (0800 GMT) was adjourned until 3 p.m. (1300 GMT) for talks on how to proceed. "There is procedural chaos," one Western envoy said.
Western diplomats said the South African amendment, though adding only five words to a two-page document, risked weakening somewhat the message to Iran that it must open up to IAEA investigations into suspected atom bomb research.
South African diplomats were not immediately available for comment but their proposed change was circulated among member states.
The proposed text says "it is essential for Iran to immediately implement" a framework deal with the IAEA to clarify concern over possible military dimensions to its nuclear programme.
South Africa's amendment would add: "once it (the framework deal) has been concluded," a formulation which Western diplomats said could dilute some of the pressure on Tehran.
"The Americans object," a second Western diplomat said.
The IAEA has tried in a series of high-profile meetings with Iran that began in January to agree a "Structured Approach" on how to conduct its investigation. IAEA chief Yukiya Amano said this week that no concrete results had been achieved, calling the lack of progress "frustrating".
The resolution can be approved by the board even without South Africa's support, but the powers are keen to ensure near unanimous backing. If South Africa objects or abstains, other NAM states may do the same, they say.
Iran says it wants to produce electricity and not bombs. Refined uranium can be used to fuel nuclear power plants. If enriched to a high degree, it can provide the explosive core for a nuclear warhead.
Israel, believed to be the Middle East's only nuclear-armed state, sees the risk of Iran developing an atom bomb as a threat to its existence and has stepped up hints of military action.
Washington says there is still time for diplomacy and sanctions to make Tehran change course.