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(CNN) —  

President Barack Obama, facing Persian Gulf countries deeply skeptical about his proposed nuclear deal with Iran, said Thursday that the U.S. would use military force if necessary to defend its Arab allies.

Obama had spent the day huddled with leaders from the region at his Camp David retreat, and emerged from their summit declaring that he was as committed as ever to protecting them from aggression, a reference to Iran.

A joint statement delivered at the end of the gathering declared that the U.S. will continue to “deter and confront external aggression against our allies and partners, as we did in the Gulf War,” and that the U.S. Is ready would work with them to determine an appropriate response in the face of such aggression, “including the potential use of military force.”

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Anxieties about Iran’s nuclear ambitions were far from abated by the end of the summit, and Obama acknowledged differences persist between himself and the oil-rich monarchies of the Gulf Cooperation Council bloc — Saudi Arabia, Kuwait, Bahrain, Oman, Qatar and the United Arab Emirates — with whom he met. But the leaders expressed optimism that enhanced defense ties would bring relations between the region and the United States to new levels.

Obama said he didn’t want to “deny the concerns” of Arab nations over the potential reduction in sanctions on Iran under the deal – which they fear will embolden Tehran – and that he wasn’t asking the nations to approve the preliminary pact reached in April.

“Given that I’m not going to sign off on any deal until I’ve seen the details of it, I wouldn’t expect them to either,” Obama said.

But he insisted that his defense of the deal – which included explanations of some of its technical details – had made a difference.

“That was important to them. And I think gave them additional confidence,” he said.

Arab leaders emerging from the summit expressed optimism that the gathering had yielded an historic boost in their ties to the U.S.

Calling the summit “unprecedented,” Saudi foreign minister Adel al Jubeir said the day had brought U.S.-Gulf ties to an “entirely different level over next decades.”

Obama, speaking to reporters at the conclusion of the summit, said his country’s relationship to the Gulf states was entering a new era based on strong defense ties.

“I was very explicit,” Obama said. “The United States will stand by our GCC partners against external attack and will deepen and extend the cooperation that we have when it comes to the many challenges that exist in the region.”

He listed specific areas the United States would commit to defending Gulf allies, including aiding in the development of a collective missile defense system.

But even the stepped-up commitments to the region stopped short of the formal mutual defense pact that some of the nations – wary of an empowered Iran – desire.

The summit comes as the Gulf Cooperation Council bloc – comprised of Saudi Arabia, Kuwait, Bahrain, Oman, Qatar and the United Arab Emirates – are particularly concerned about an emerging U.S. deal with Iran over its nuclear program, which they worry will empower arch-foe Tehran.

The statements from Obama at the conclusion of the summit outlined U.S. commitments to the GCC, including expediting arms transfers to the region, staging a new large-scale military exercise against terror and cyber attacks, and forming a new partnership to improve counterterrorism and missile defense cooperation.

U.S. officials hoped the wooded setting in the Catoctin Mountains would foster a relaxed dynamic in the discussions, which have also included Secretary of State John Kerry, Defense Secretary Ashton Carter and Energy Secretary Ernest Moniz, who is steeped in the details of the Iran nuclear deal.

Before the summit began, Arab diplomatic officials said the Gulf states themselves had decided to cool the temperature and accentuate the positive in meetings with the U.S. officials.

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The gulf countries have been seeking a more significant upgrade of their security alliance than the U.S. is willing to confer, despite the planned U.S. boost to arms, training and other security measures.

The GCC foreign ministers met Tuesday night and agreed that, though they weren’t getting everything they wanted from the U.S., they are going to build on what they are getting. They want this to be the first of a regular summit, with the next one in Riyadh, Saudi Arabia, next year.

Obama, speaking Thursday, said he had committed to attending a future GCC summit, though didn’t specify where.

Still, the lack of participation by GCC leaders has been widely perceived as a sign that many of its members are displeased with what the U.S. is offering and want to convey displeasure at various administration policies, including talks with Iran over its nuclear program.

Only the leaders of Qatar and Kuwait attended, with the king of Saudi Arabia canceling at the last minute and Bahrain’s king attending the Royal Windsor Horse Show outside London. While there, he is expected to meet with Queen Elizabeth II.