Secretary of State John F. Kerry and Saudi Arabia’s foreign minister, Prince Saud al-Faisal, give a news conference in Riyadh on March 5, 2015. (Ahmed Yosri/EPA)

Secretary of State John F. Kerry assured Arab allies on Thursday that Washington will work with them to counter Iranian influence in the region even if a deal is struck over Tehran’s nuclear program.

Kerry’s meetings in Saudi Arabia — a day after wrapping up the latest round of nuclear negotiations with Iran in Switzerland — reflect efforts to persuade Arab states in the Persian Gulf that a deal with Tehran is the best option to monitor and limit its nuclear program.

At the same time, the gulf states want a commitment from Washington that it will not soften its opposition to what they see as Iran’s increasing aggressiveness in the region, including in Yemen, where rebels apparently backed by Tehran toppled the U.S.-allied government in January.

Referring to Iran, Kerry said in an appearance with the Saudi foreign minister, Prince Saud al-Faisal, “The first step is to make sure they don’t have nuclear weapons.”

“Nothing else changes on the next day with respect to our joint commitment to stand up against any kind of interference or violation of international law or support for terrorism,” Kerry added.

Graphic: Iran's potential nuclear capability

Details of the talks with Iran have not been made public. But critics of the dialogue, including Israeli Prime Minister Benjamin Netanyahu, claim a potential deal would leave Iran with enough uranium-enrichment capability to possibly push toward nuclear weapons in the future.

Such a scenario, they insist, could touch off a nuclear arms race among the gulf’s Arab states, which worry about Iran’s expanding influence in places such as Iraq and Yemen.

Iran insists it does not seek nuclear arms, which the country’s supreme religious and political leader has declared are forbidden by Islam, but wants the capacity to make nuclear fuel for reactors that produce energy and medical isotopes.

[Read: Poll suggests American back nuclear deal with Iran]

Kerry’s one-day visit to Riyadh underscores that Israel is not the only country in the Middle East leery of how a deal with Iran may upend the balance of power.

“We see Iran involved in Syria and Lebanon and Yemen and Iraq and God knows where,” the Saudi foreign minister said. “This . . . must stop if Iran is to be part of the solution of the region and not part of the problem.”

But the Western-allied gulf nations, meanwhile, also are widening their reach in the region.

Saudi Arabia and other gulf states strongly back Syrian rebels seeking to topple the Iranian-linked government of Syrian President Bashar al-Assad. And the United Arab Emirates has joined U.S.-led airstrikes against the Islamic State, the al-Qaeda offshoot that has taken over parts of Iraq and Syria.

“Even as we are engaged in discussions with Iran, we will not take our eye off Iran’s other destabilizing actions in places like Syria, Lebanon, Iraq and the Arabian Peninsula, Yemen particularly, whether or not we reach a deal on Iran’s nuclear program,” Kerry said.

In the morning, he met with King Salman, the new Saudi monarch, at his “farm,” an opulent desert palace in an area filled with palm trees.

Kerry and Saud walked through a courtyard lined with sofas and carpets, the air heavy with incense, and into a long room where the king waited.

Later, Kerry went to Riyadh Air Base, at the edge of the capital, for talks with the foreign ministers of nations that are part of the Gulf Cooperation Council: the United Arab Emirates, Kuwait, Oman, Qatar, Bahrain and Saudi Arabia.

Senior State Department officials said Kerry sought to allay their concerns that Iran could build nuclear weapons at the end of a deal with a 10-year or longer time frame.

Kerry also intended to assure them that Washington has not changed its position on other security issues related to Iran, such as its support for Assad and backing for Yemen’s Houthi rebels, who now control Sanaa, the capital. The Houthis belong to the Zaydi sect of Shiite Islam, giving them an affinity with Shiite-led Iran.

“So if we have an agreement” on Iran’s nuclear program, said a State Department official, speaking on the condition of anonymity under agency rules, “our view is that is something that will contribute directly to regional stability, as well as global security and stability.”

The official added that deal or no deal, “we will continue to confront aggressively Iranian expansion in the region, Iranian aggressiveness.”

In Switzerland, China’s envoy to the six-nation group engaged in the nuclear talks told reporters that the negotiations could be moving into the “final stage,” with all sides seeking to reach a preliminary framework by the end of the month.

“Basically, there are two categories of issues,” said Wang Qun, director general of the arms control department of China’s Ministry of Foreign Affairs. “One is how to see the nonproliferation concern is removed, and secondly is to see the Iranian rights for peaceful uses [of nuclear technology] is ensured.”

Iran has been conducting the talks with the five permanent members of the U.N. Security Council — the United States, Russia, China, Britain and France — plus Germany.

Talks are scheduled to resume March 15.

“And we expect soon thereafter to know if Iran is willing to make the tough choices needed,” said Kerry, who plans meetings in Paris with European allies on Saturday.

Brian Murphy in Washington contributed to this report.