WASHINGTON — US President Barack Obama said Israeli officials now recognize the efficacy of last year’s nuclear deal with Iran, citing the backing of Jerusalem, among the accord’s staunchest critics, as he defended the agreement with Tehran and denied “nefarious” motives in the transfer of money to the Islamic Republic.

Israeli defense officials are now behind the deal, Obama said at a Pentagon press conference, where he also continued to attack Republican presidential candidate Donald Trump and admitted Islamic State remained a threat despite setbacks suffered by the terror group.

In defense of the US-led deal with Iran reached last summer, which aims to curb Tehran’s nuclear development in exchange for sanctions relief, the president said, “By all accounts, it has worked exactly the way we said it was going to work.”

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The “Israeli military and security community … acknowledges this has been a game changer,” he said. “The country that was most opposed to the deal.”

Some high-level former and current Israeli defense figures have spoken out in sometimes conditional defense of the nuclear deal. Chief of staff Gadi Eisenkot said warily in January that it could present “opportunities” in the future but also raised concerns at the “challenges” it poses. And lawmakers from the ruling coalition have continued to criticize the agreement, citing continued ballistic missile tests banned under an attendant UN agreement, and pointing to Tehran’s continued anti-Israel rhetoric and support for terror groups. Israel’s Prime Minister Benjamin Netanyahu remains openly critical of the agreement, which he says paves Iran’s path to a nuclear arsenal.

The nuclear agreement “removes the restrictions on Iran’s nuclear program based on dates certain, rather than on changes in Iran’s aggressive behavior, including its support for terrorism around the world,” a senior Israeli official told The Times of Israel two weeks ago. “The deal doesn’t solve the Iranian nuclear problem, but rather delays and intensifies it.”

The accord, which began its formal implementation in January, will expire in 15 years.

Obama also said those who had been most critical of the deal should make mea culpas and admit they were wrong.

“What I’m interested in is if there’s some news to be made, why not have some of these folks who were predicting disaster come out and say, ‘This thing actually worked.’ Now that would be a shock,” he said.

“That would be impressive. If some of these folks who said the sky is falling suddenly said, ‘You know what? We were wrong and we are glad that Iran no longer has the capacity to break out in short term and develop a nuclear weapon.’ But that wasn’t going to happen.”

The president’s defense of the year-old accord came as his administration has sought to downplay a day-old Wall Street Journal report that the US sent a plane loaded with $400 million of cash to Iran during a January prisoner exchange.

“This wasn’t some nefarious deal,” Obama said.

The report centered around Obama authorizing a $1.7 billion payment to Tehran in January, around the same time four American hostages were released, including Washington Post correspondent Jason Rezaian.

The settlement was to settle a failed 1979 arms deal in which Iran paid for weapons that were not delivered after the Shah was overthrown.

Obama emphasized that the United States does “not pay ransom for hostages” and that the payoff in question was not a ransom for the four detainees, echoing comments from Secretary of State John Kerry.

He pointed out that the payment, which will include an additional $1.3 billion in interest to be paid later, was announced by the administration when the agreement was concluded in January, a day after the implementation of a landmark nuclear agreement with Iran. “It wasn’t a secret. We were completely open about it,” he said.

Obama allowed that the one piece of new information was that the $400 million was paid in cash. It was delivered to Iran on palettes aboard an unmarked plane.

“The only bit of news is that we paid cash,” he said. “The reason is because we couldn’t send them a check and we couldn’t wire the money. We don’t have a banking relationship with Iran which is part of the pressure we applied on them.”

The State Department announced the payment on January 17, a day after the Tehran released four American hostages, which was also on the same weekend sanctions on Iran were lifted.

The payment has revived allegations from Trump and other critics of the Iran nuclear deal.

Obama also answered political questions at the news conference, pushing back at Trump’s suggestions that the November election might be rigged, calling the assertion “ridiculous.”

He said his advice to Trump, a candidate he has declared “unfit” for the presidency, was to “go out there and try to win the election.”

Also, in regard to the presidential race. Trump and Democratic nominee Hillary Clinton will soon be receiving classified briefings, giving them access to sensitive information about national security and America’s military posture. Asked whether he was worried about Trump having access to such material, Obama said simply that those who want to be president need to start acting like it.

“That means being able to receive these briefings and not spread them around,” he said.

The president’s appearance before reporters followed an hours-long meeting with military leaders at the Pentagon on the fight against the Islamic State group.

Obama said there have been gains in weakening IS in Iraq and Syria, but he conceded the extremist group still poses a threat to the United States as it shifts its tactics to carrying out attacks elsewhere around the world. While those attacks may result in less carnage, Obama said IS knows they still create “the kinds of fear and concern that elevates their profile.”

The rise of the Islamic State has kept Obama tied to the Middle East in a way he had hoped to avoid in his eighth and final year in office. While the US has far fewer troops in the region than when he took office in 2009, Republicans argue that the drawdown of troops from Iraq created a vacuum that allowed the Islamic State to thrive.

Asked whether he feels any personal disappointment about not being able to do more to stop the Islamic State, Obama said “I haven’t gotten numb to it. It bugs me.”

On Syria, the president criticized Russia’s support of government attacks against opposition forces and its sieges of cities such as Aleppo. He accused Russia of failing to take steps to reduce violence in Syria — where a civil war has raged for much of Obama’s presidency — but said the US would continue trying to push Moscow to focus on the fight against IS and other extremists.