President Barack Obama defended a framework nuclear agreement with Iran as a "once-in-a-lifetime opportunity" to prevent a nuclear bomb and bring longer-term stability to the Middle East.

In a weekend interview with The New York Times published Sunday, the president insisted the United States would stand by Israel if it were to come under attack, but acknowledged that his pursuit of diplomacy with Tehran has caused strain with the close ally.

"It's been a hard period," Obama said, adding it is "personally difficult" for him to hear his administration accused of not looking out for Israel's interests.

Now in his seventh year in office, Obama cast the Iran talks as part of a broader foreign policy doctrine that sees American military power as a safeguard that gives him the ability to take calculated risks.

New approach

"We are powerful enough to be able to test these propositions without putting ourselves at risk," he said, citing his overtures to Cuba and Myanmar, formerly known as Burma, as other examples of his approach.

The president's comments come days after the U.S. and other world powers reached a tentative agreement to curb Iran's nuclear program in exchange for sanctions relief. The framework cleared the way for negotiators to work out technical details ahead of a June 30 deadline for a final deal.

'We are powerful enough to be able to test these propositions without putting ourselves at risk.' - U.S. President Barack Obama on U.S. strategy

Obama argued that successful negotiations presented the most effective way to keep Iran from obtaining a nuclear weapon, but insisted he would keep all options on the table if Tehran were to violate the terms.

"I've been very clear that Iran will not get a nuclear weapon on my watch, and I think they should understand that we mean it," Obama said. "But I say that hoping that we can conclude this diplomatic arrangement — and that it ushers a new era in U.S.-Iranian relations — and, just as importantly, over time, a new era in Iranian relations with its neighbours."

The president said there are many details that still need to be worked out with the Iranians, and cautioned there would be "real political difficulties" in implementing an agreement in both countries. He reiterated his opposition to legislation that would give the U.S. Congress final say in approving or rejecting a deal, but said he hoped to find a path to allow Congress to "express itself."

The White House plans an aggressive campaign to sell the deal to Congress, as well as to skeptical Arab allies who worry about Iran's destabilizing activity in the region. The president has invited leaders of six Gulf nations to Washington this spring and said he wanted to "formalize" U.S. assistance.

'International mechanism'

On the substance of the Iran framework agreement, Obama outlined more specifics of how the U.S. would seek to verify that Tehran wasn't cheating. He said there would be an "international mechanism" that would assess whether there needed to be an inspection at a suspicious site and could overrule Iranian objections.

The nuclear talks have marked a remarkable shift in the frozen relationship between the U.S. and Iran. It has become normal for officials from both countries to communicate and hold face-to-face meetings. Obama is yet to meet with Iranian President Hasan Rouhani, though they did speak on the phone. He has also exchanged letters with Iran's Supreme Leader Ayatollah Ali Khamenei.

Obama said the letters include "a lot of reminders of what he perceives as past grievances against Iran."

But he said the concessions Khamenei allowed his negotiators to make in the nuclear talks suggest "he does realize that the sanctions regime that we put together was weakening Iran over the long term, and that if in fact he wanted to see Iran re-enter the community of nations, then there were going to have to be changes."