DOHA, Qatar—Gulf Arab states on Monday cautiously backed the Obama administration's nuclear agreement with Iran, giving the White House a potentially important diplomatic win as it seeks to build support for its signature foreign policy initiative.

The positive response from the Gulf Cooperation Council—which is comprised of Saudi Arabia, Qatar, the United Arab Emirates, Kuwait, Oman and Bahrain—followed months of intense lobbying by the White House that included offers of increased arms sales, intelligence-sharing and military training.

Secretary of State John Kerry held a daylong summit on Monday with the council's foreign ministers to explain the terms of the nuclear agreement and the need for increased cooperation between Washington and the GCC to guard against Iran expanding its influence in the region.

"This was the best option amongst other options in order to try to come up with a solution for the nuclear weapons of Iran though dialogue, and this came up as a result of the efforts exerted by the United States of America and its allies," Qatar Foreign Minister Khalid al-Attiyah said at a joint news conference with Mr. Kerry at the end of meetings in Qatar's capital. The Persian Gulf monarchy currently serves as the chair of the GCC.

He said the GCC countries have welcomed the plan Mr. Kerry laid out. "He let us know that there's going to be a kind of live oversight for Iran not to gain or to get any nuclear weapons," he said. "This is reassuring to the region."

President Barack Obama is locked in a fierce political battle in Washington to drum up support on Capitol Hill for the nuclear deal, which limits parts of Iran's nuclear program in exchange for the lifting of international sanctions.

Republicans and pro-Israel politicians are fiercely opposed to the agreement, arguing it will undermine the security of Washington's key Middle East allies, including Israel, Saudi Arabia and the United Arab Emirates.

They also charge that Tehran will use tens of billions of dollars in new oil money and revenues to fund its militant proxies in the region, including the Assad regime in Syria, Hezbollah in Lebanon, and the Houthis in Yemen.

Congress is currently conducting a 60-day vetting period of the deal and will vote in September on whether to endorse or reject it.

Israeli Prime Minister Benjamin Netanyahu has publicly attacked the nuclear deal and pressed American lawmakers to vote against it. Saudi, Emirati and Qatari officials have privately groused about the deal and voiced concerns that Washington may weaken its decades-old alliance with the Gulf states as it pursues a rapprochement with Tehran, their regional rival.

The GCC's public backing of the Iran deal could undercut criticism of the White House and leave Israel more isolated on the diplomatic stage. Mr. Kerry was quick on Monday to present a common front with the Gulf Arab states.

"Ministers agreed…that once fully implemented, the [nuclear deal] contributes to the region's long-term security, including by preventing Iran from developing or acquiring a military-nuclear capability," Mr. Kerry said at his appearance with Mr. Attiyah. "But frankly, most of the time that we spent this afternoon was spent articulating and working on the full measure of the relationship between the U.S. and the GCC going forward."

Mr. Kerry is on a regional trip through the Middle East and Asia, which didn't include a stop in Israel. Israeli officials have voiced a wariness of engaging with the Obama administration during the congressional review period, due Mr. Netanyahu's strident opposition to the deal.

Write to Jay Solomon at jay.solomon@wsj.com

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