By Jeff Mason, Francois Murphy and Parisa Hafezi

WASHINGTON/VIENNA/DUBAI (Reuters) -U.S. President Donald Trump said on Thursday an Israeli strike on Iran "could very well happen," and a senior Israeli official told the Wall Street Journal it could occur as soon as Sunday unless Iran agrees to halt production of material for an atomic bomb.

U.S. intelligence has indicated that Israel has been making preparations for a strike against Iran's nuclear facilities, and U.S. officials have said on condition of anonymity that Israel could attack in the coming days.

The Wall Street Journal report was the first suggestion of a potential date for an Israeli strike on its longtime foe Iran as Israel tries to block Tehran from developing a nuclear weapon.

Trump on Thursday reiterated his hopes for a peaceful end to the tensions, and there was counter-speculation that the threat of an Israeli attack was a tactic intended to pressure Iran into concessions on its nuclear program at the negotiating table.

"We remain committed to a Diplomatic Resolution to the Iran Nuclear Issue!" Trump wrote on his Truth Social platform.

"My entire Administration has been directed to negotiate with Iran. They could be a Great Country, but they first must completely give up hopes of obtaining a Nuclear Weapon," he added.

Tensions have been building as Trump's efforts to reach a nuclear deal with Iran appear to be deadlocked.

U.S. and Iranian officials were scheduled to hold a sixth round of talks on Tehran's escalating uranium enrichment programme in Oman on Sunday, according to officials from both countries and their Omani mediators.

Speculation about an Israeli attack has raised fears that such a move could spark a regional war and retaliatory strikes from Iran, which has vowed to destroy Israel.

Axios reported on Thursday that the White House has told Israel the U.S. will not be directly involved in any Israeli strike on Iranian nuclear facilities, quoting two U.S. sources and an Israeli source familiar with the discussions.

Analysts have said Israel is unlikely to act without U.S. support, citing past threats on Iran that fizzled out without Washington's backing.

The Wall Street Journal said the U.S. would not provide "offensive assistance" to Israel for an attack on Iran.

While the U.S. could still aid Israel with intelligence or logistics support as well as help defend Israel if Iran strikes back, it was unclear how the reported U.S. unwillingness to participate directly might influence Israeli decision making.

Axios said a solo Israeli operation would be more limited because its air force does not have bombers that can carry the bunker buster bombs needed to hit Iran's Fordow underground uranium enrichment facility.

IRAN IN BREACH, UN BODY SAYS

The U.N. nuclear watchdog's board of governors on Thursday declared Iran in breach of its non-proliferation obligations, and Tehran announced counter-measures. A senior Iranian official said a "friendly country" had warned it of a potential Israeli attack.

Security concerns have risen since Trump said on Wednesday that U.S. personnel were being moved out of the region because "it could be a dangerous place" and that Tehran would not be allowed to develop a nuclear weapon.

Israeli Prime Minister Benjamin Netanyahu raised the possibility of strikes in a phone conversation with Trump on Monday, the Journal reported, citing two U.S. officials.

"I don't want to say imminent, but it looks like it's something that could very well happen," Trump told reporters at a White House event earlier on Thursday, adding Iran could not be allowed to develop a nuclear weapon.

"I'd love to avoid the conflict," he said. "Iran's going to have to negotiate a little bit tougher, meaning they're going to have to give us something they're not willing to give us right now."

Security in the Middle East has already been destabilised by spillover effects of the Gaza war between Israel and Palestinian militant group Hamas.

Trump has threatened to bomb Iran if the nuclear talks do not yield a deal and said he has become less confident Tehran will agree to stop enriching uranium. The Islamic Republic wants a lifting of U.S. sanctions imposed on it since 2018.

Trump on Thursday also expressed frustration that oil prices had risen amid supply concerns arising from potential conflict in the Middle East.

With Washington offering little explanation for its security concerns, some foreign diplomats suggested that the evacuation of personnel and U.S. officials anonymously raising the spectre of an Israeli attack could be a ploy to ratchet up pressure on Tehran for concessions at the negotiating table.

A senior Iranian official told Reuters on Thursday the latest tensions were intended to "influence Tehran to change its position about its nuclear rights" during the Sunday talks.

Iranian President Masoud Pezeshkian said that even if the country's nuclear facilities were destroyed by bombs they would be rebuilt, state media reported on Thursday.

BREACH OF NON-PROLIFERATION OBLIGATIONS

The International Atomic Energy Agency's Board of Governors declared Iran in breach of its non-proliferation obligations for the first time in almost 20 years, raising the prospect of reporting it to the U.N. Security Council.

The step is the culmination of a series of stand-offs between the IAEA and Iran since Trump pulled the U.S. out of a nuclear deal between Tehran and major powers in 2018 during his first term, after which that accord unravelled.

An IAEA official said Iran had responded to the 35-nation board's declaration by informing the U.N. watchdog that it plans to open a third uranium enrichment plant.

Enrichment can be used to produce uranium for reactor fuel or, at higher levels of refinement, for atomic bombs. Iran says its nuclear energy programme is only for peaceful purposes.

(Additional reporting by Yousef Saba and Dubai newsroom, Marc Jones in London, GV De Clercq in Rome, Jeff Mason, Jarrett Renshaw, Humeyra Pamuk, Gram Slattery and Idrees Ali in Washington, Alexander Cornwell in Jerusalem; writing by Timothy Heritage, Michael Georgy, Matt Spetalnick and Deepa Babington; editing by Mark Heinrich, Deepa Babington and Cynthia Osterman)