By Maayan Lubell

JERUSALEM (Reuters) -Israel sent Mossad commandos deep into Iran to destroy Iranian weapons systems during Israel's attack on nuclear and military targets, an Israeli security source said, while another official said Israel used a ploy to suggest the strike was not imminent.

The Israeli officials, speaking on condition of anonymity because of the clandestine nature of the operations, described secret and lengthy preparations that went into an attack that sent oil prices sharply higher on fears of regional escalation.

Reuters could not independently verify the accounts.

Iranian officials who spoke to Reuters shortly before the attack had been dismissive about any imminent action and repeatedly said talk of strikes was just "psychological pressure" to influence U.S.-Iranian nuclear negotiations that were due on Sunday.

Iran has not given a detailed account of what its Foreign Minister Abbas Araghchi called "unlawful and cowardly attacks", but it has promised a harsh response. Iran's mission at the United Nations did not immediately respond to a request for comment on Israel's covert operation and other subterfuge related to the attacks.

Ahead of the strike, Israel gave the impression its focus was still on U.S. diplomacy towards a nuclear deal with Iran, briefing journalists that its spy chief would go to Washington before the next negotiations.

Instead, Israel said it sent 200 warplanes to conduct a wave of air strikes across Iran before dawn on Friday, hitting nuclear facilities and missile factories, and killing military commanders and nuclear scientists, in a culmination of its efforts to prevent Iran from obtaining a nuclear weapon.

Iran says its nuclear programme is purely civilian.

The Israeli security source said Israel's military and Mossad had worked for years on the intelligence needed for the strikes, which killed the commander of Iran's Revolutionary Guards Corps among others.

The security source said Mossad commandos had covertly deployed weapons across Iran, including explosive drones that were launched at a surface-to-surface missile base near Tehran.

The Mossad commandos also fired precision-guided weapons systems at Iranian surface-to-air missile systems as the Israeli attack got underway, reducing the threat to Israeli warplanes.

A grainy black and white video distributed by Mossad showed what it said were the organization's operational force - two camouflaged figures crouched in what looks like desert terrain, deploying the precision weapons system meant to destroy Iran's air defence systems.

Some of the operation's components would have taken years to be put together, said Sima Shine, a former chief Mossad analyst and now a researcher at Israel's Institute for National Security Studies (INSS).

The decision to strike Iran was made on Monday, the same day Israeli Prime Minister Benjamin Netanyahu and U.S. President Donald Trump spoke by phone, when Netanyahu, Defence Minister Israel Katz and military chief Eyal Zamir decided the operation would begin on Friday, said a second source, an Israeli defence official.

    Their discussion was held after the conversation between Trump and Netanyahu, a third official, close to Netanyahu, said.

PRESS BRIEFINGS

The final green light was given by Netanyahu's security cabinet, which convened on Thursday night.

    In the days leading up to the strikes, Israel played out a ploy to create the impression an attack was not imminent, according to a fourth source, also an Israeli official.

    False reports suggesting that a rift between Israel and the United States had emerged during Netanyahu and Trump's phone call on Monday were not denied, the fourth source said.      

    A press release about a visit by Katz, Zamir and the head of Israel's Air Force Tomer Bar to an air force base mentioned Gaza, Yemen and Lebanon - but not Iran.

    The fourth source said that the ruse included misleading information given in press briefings. As the attack unfolded in the early hours of Friday, some Israeli journalists pointed to one such briefing, according to which Strategic Affairs Minister Ron Dermer and Mossad Head David Barnea were to be sent to Washington ahead of the next round of nuclear talks on Sunday.

Dermer later appeared seated with Netanyahu at Israel's defence headquarters bunker in Tel Aviv, in a video distributed by the prime minister's office.

A fifth, military source said that Israel had been able to surprise Iran but since the operation was not over, there could be "difficult days" ahead.

Iran, which fired ballistic missiles at Israel when they traded blows last year, has promised "harsh punishment" in response to the attack. Israel said it had intercepted many of the 100 drones launched towards Israeli territory in retaliation.

(Reporting by Maayan Lubell; Writing by Tom Perry; Editing by Aidan Lewis)