* Resolution overwhelmingly approved by 35-nation IAEA board
* Six world powers sought broad backing for rebuking Tehran
* Keen for diplomatic breakthrough to avert threat of war
* Iran: IAEA governors' vote "complicates situation"
* Iran's "procrastination unacceptable," EU says
By Fredrik Dahl
VIENNA, Sept 13 (Reuters) - The 35-nation board of the U.N. nuclear watchdog censured Iran on Thursday for defying international demands to curb uranium enrichment and failing to address mounting disquiet about its suspected research into atomic bombs.
Two days after Israel ramped up threats to attack its arch-enemy Iran, the board overwhelmingly passed a resolution voicing "serious concern" about Tehran's nuclear advances but also making clear its desire for a peaceful resolution of the row.
Russia and China joined four U.S.-led Western powers in sponsoring the resolution to display big power unity on Iran.
Only Cuba voted against. Three countries, including Egypt, abstained, according to diplomats who took part in the closed-door meeting at International Atomic Energy Agency (IAEA) headquarters in Vienna.
"The diplomatic pressure on Iran is increasing. The isolation is increasing," U.S. envoy Robert Wood said.
But Iran's envoy to the IAEA, Ali Asghar Soltanieh, said such resolutions were counterproductive. Iran has sallied ahead with its nuclear programme despite a series of similar resolutions since 2006 as well as harsh economic sanctions.
The difference now, though, is that the need for a diplomatic breakthrough is becoming urgent given Israel's increasingly strident demand that Iran be set a deadline to cooperate or risk the Jewish state launching air strikes that many fear could ignite a devastating Middle East war.
"It (the IAEA resolution) will only complicate the situation and jeopardise the cooperative environment which we desperately need," Soltanieh told reporters after the vote.
The resolution faults Iran for ignoring U.N. Security Council calls on it to suspend uranium enrichment - a conduit to producing fuel for nuclear power stations or bombs - and open up to investigations of signs that it seeks nuclear arms know-how.
Six world powers had tabled a resolution text on Wednesday, aiming to raise pressure on Iran to relent, a day after Israel signalled it was almost out of patience with the use of diplomacy and sanctions to try to rein in the Islamic Republic.
South Africa, like Iran a member of the Non-Aligned Movement of mostly developing nations, earlier plunged the meeting into confusion by putting forward an amendment which some Western diplomats said might have weakened the language towards Iran.
But a compromise was hammered out during a three-hour adjournment of the meeting, the diplomats said, satisfying the United States, Russia, France, China, Britain and Germany.
The amendment concerned a section of the text demanding that Iran immediately implement a yet-to-be agreed framework accord with the IAEA on how the agency should conduct its investigation into suspected nuclear explosives research in the Islamic state.
The compromise changed the original text but not as far as the South African proposal, easing Western fears that it could lower the heat on Tehran to come clean with IAEA sleuths.
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 carry out its inquiry. IAEA Director-General Yukiya Amano said this week that no concrete results had been achieved, calling the lack of progress "frustrating".
"Iran has not engaged seriously and without preconditions in talks aimed at restoring international confidence in the exclusively peaceful nature of its nuclear programme," the 27-nation European Union said in a statement to the board.
"Iran's procrastination is unacceptable," the bloc said.
Wood, the U.S. envoy, accused Iran of "systematically demolishing" a facility at the Parchin military site that IAEA inspectors want to visit as part of their investigation.
"Iran has been taking measures that appear consistent with an effort to remove evidence of its past activities at Parchin," he told the board gathering.
Soltanieh dismissed what he called the "noise about cleaning" and "distorted information" about Parchin, a vast military complex southeast of Tehran where the IAEA suspects Iran has carried out explosives tests relevant for atom bombs.
Iran says it wants to produce electricity from enriched uranium 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 danger of Iran developing an atom bomb as a threat to its existence and has stepped up hints of air strikes on Iranian nuclear installations.
But Benjamin Netanyahu's deputy for intelligence and atomic affairs, Dan Meridor, on Thursday publicly disagreed with the Israeli prime minister's call for Iran to be confronted with a "red line" beyond which its disputed nuclear programme would face military attack.
He called for international sanctions against Tehran to be intensified "so it understands that the price it is paying is mounting and that the only way to be rid of it is to stop the (nuclear) race, to arrive at an agreement, or an international understanding, that it is calling it quits".
Meridor, part of Netanyahu's inner security cabinet, took a more moderate view of a nuclear-armed Iran than the premier, who has likened that prospect to a second Holocaust.
"I don't want to speak in apocalyptic ... Holocaust terms," said Meridor. "I think that we are strong and we will overcome the challenges, but this is a serious challenge."
The United States, Israel's main ally, says there is still time for diplomacy and sanctions to make Iran, one of the world's largest oil exporters, change course.