Secretary of State John F. Kerry said Monday that he hopes to have an agreement to end a dispute over Iran's nuclear program within months. (REUTERS)

Secretary of State John F. Kerry, defending a potential nuclear deal with Iran, extolled President Obama on Monday as a strong foreign policy leader and a “man of his word,” whose guarantee that Iran will never be allowed to obtain a nuclear weapon should be heeded by doubters.

“Every time the president has said, ‘I’m going to do something,’ he has done it,” Kerry said at a news conference with the United Arab Emirates foreign minister, Abdullah bin Zayed al-Nahyan. Obama’s Iran pledge, he said, “is a centerpiece of his foreign policy, and he will not bluff.”

Kerry’s remarks were clearly directed both at Israel, which has launched an international campaign to stop the possible nuclear deal with Iran from being finalized, and U.S. lawmakers who charge that the agreement would harm American and Israeli security.

High-level negotiations over the weekend in Geneva were suspended, Kerry said, after Iranian Foreign Minister Mohammad Javad Zarif said he needed further consultations with Tehran. The deal, an interim, confidence-building step in which disputed Iranian nuclear programs would be frozen in exchange for a partial lifting of international sanctions, remains in draft form.

Zarif on Monday directly contradicted Kerry’s public remarks about how the Geneva talks were suspended, disputing his assertion that Iran walked away from a deal offered by the United States and five other major powers.

“No amount of spinning can change what happened,” Zarif wrote in one of a series of Twitter postings that blamed internal divisions among the Western powers for the suspension of the talks. “Mr. Secretary, was it Iran that gutted over half of US draft Thursday night?”

Later, in an interview broadcast on Iranian television, Zarif suggested that Kerry’s characterization of the talks “damages confidence” among the negotiators.

The outcome in Geneva already has provided ammunition to Obama administration critics at home and abroad.

Since Kerry briefed him on the Iran proposal during a visit to Israel last week, Prime Minister Benjamin Netanyahu has repeatedly called it “a bad deal.” Netanyahu’s government has urged lawmakers and Jewish groups around the world to lobby against it.

Saudi Arabia, which sees Iran as its principal rival and threat in the region, said it accepted Obama’s assurances, but the kingdom warned Kerry against a “partial deal” when he visited there last week.

And Congress is considering legislation to strengthen, not ease, sanctions against Iran. Sen. Lindsey O. Graham (R-S.C.) predicted Sunday that “a new round of sanctions will be coming.”

As it tries to seal the deal before opponents can derail it, the administration is launching its own sales effort. In addition to lobbying foreign leaders, Kerry will begin a round of congressional consultations this week.

Separately, Iran signed an agreement Monday with the United Nations nuclear watchdog agency in which it pledged to allow greater access to some of its nuclear sites, U.N. officials confirmed.

Under the accord, Iran agreed to give IAEA inspectors some access to the country’s main uranium mine and to a plant that produces heavy water, which would be used for nuclear reactor under construction near the city of Arak. Iranian officials also agreed to provide information about additional nuclear facilities the government has said it plans to build.

On the final leg of a 10-day trip to seven countries, Kerry said criticism of the proposed Iran accord is premature and ill-informed.

“I believe the [Israeli] prime minister needs to recognize that no agreement has been reached about the endgame here. That’s the subject of the negotiation,” he said.

The specific terms of the interim deal — which would remain in place while negotiations continued over the permanent, verifiable elimination of any Iranian nuclear weapons capability and the lifting of all sanctions — remain secret. There are questions about the extent to which it would allow Iran to continue low-level uranium enrichment and construction of its Arak heavy-water reactor, as well as the scope of sanctions relief.

The Arak reactor, ostensibly designed for medical research and isotope production, has raised proliferation concerns because its spent nuclear fuel could be reprocessed to extract plutonium. Highly enriched uranium and plutonium can be used as fissile material in nuclear weapons. Iran has denied any plans to build nuclear weapons.

“Iran has said that its program is peaceful,” Kerry said. “The supreme leader [Ayatollah Ali Khamenei] says he has issued a fatwa, the highest form of Islamic prohibition against some activity, and he said that is to prohibit Iran from ever seeking a nuclear weapon. What we are seeking to do is transform that fatwa into a legal code that universally is acceptable so that we can, in fact, prove that the program is peaceful.”

When the talks adjourned, “we were very, very close — actually, extremely close,” Kerry said in a Monday interview with the BBC.

Negotiations are scheduled to resume in Geneva on Nov. 20.

Israel’s position is that sanctions should remain fully in place until Iran stops all uranium enrichment, dismantles its centrifuges, gets rid of its stockpiles of enriched uranium and stops construction of the Arak plant.

U.S. officials believe that is unrealistic, at least in the interim deal. There is no right to or prohibition against enrichment for peaceful purposes in international nuclear conventions, Kerry told the BBC. “Some countries do; some don’t.”

“What is clear is no nuclear weapons program, and [that] you cannot have the ability to suddenly break out and have that kind of weapon without people knowing it,” he said. “So there are a whole series of standards that have to be met here.”

In his news conference, Kerry said that since the purpose of sanctions is to force negotiations, Iran’s new willingness to deal should be fully tested.

“Having a negotiation does not mean you have given up anything,” he said. “It means you will put to the test . . . whether or not Iran is prepared to do what is necessary to prove that its program can only be a peaceful program.”

As he responded to questions, Kerry launched an unbidden but spirited defense of Obama’s overall foreign policy stewardship.

“President Obama is a man of his word,” he said. Promises have been fulfilled in Iraq, Libya and Afghanistan; in killing Osama bin Laden and pursuing terrorists in Yemen and Somalia; and in dismantling Syria’s chemical weapons, he said.

Obama “will continue to defend his friends and allies in this region . . . against external attack,” Kerry said.

William Booth in Jerusalem and Joby Warrick in Washington contributed to this report.