President Obama announced expanded military ties with Persian Gulf nations on Thursday, as he sought to assure the anxious Arab allies that the U.S. would help protect their security in the face of mounting regional unrest and concerns about Iran's growing influence.

At the close of a Camp David summit, Obama vowed a "new era of cooperation." He pledged a fast-track for transfers of arms and missile defense systems, as well as expanded joint military training and other programs.

And though he did not declare a new formal security pact with the partners, he reiterated that current agreements allow the U.S. to use military force in aid of its allies if necessary. And he offered assurances that an international nuclear agreement with Iran would not leave the nations of the Gulf Cooperation Council more vulnerable.

Obama spoke in a press conference following talks with members of the Gulf State Cooperation Council, which includes Saudi Arabia, Qatar, United Arab Emirates, Kuwait, Oman and Bahrain. He was seeking to placate those countries' concerns over whether the U.S. is committed to helping protect their security, in a time of "extraordinary changes and some great challenges."

"I was very explicit ... that the United States will stand by our GCC partners against external attack," Obama told reporters.

In a joint statement with the GCC issued right after the talks, the White House said current security agreements would hold no matter the outcome of an Iranian nuclear deal. The remarks spoke directly to fears that Iran might pursue an offensive policy against its regional rivals if economic sanctions are eventually lifted, freeing up resources for a more aggressive military posture.

"In the event of such aggression or the threat of such aggression, the United States stands ready to work with our GCC partners to determine urgently what action may be appropriate, using the means at our collective disposal, including the potential use of military force, for the defense of our GCC partners," the statement said.

"The United States is prepared to work jointly with the GCC states to deter and confront an external threat to any GCC state's territorial integrity that is inconsistent with the UN Charter."

He said he updated the partners on current negotiations with Iran, and they all agreed that a comprehensive resolution is in everyone's security interests, "including the GCC partners'."

But uncertainty about the U.S. commitment to their interests in light of the Iran deal has fueled some tension among these nations. Just two other heads of state -- the emirs of Qatar and Kuwait -- joined Obama at Camp David, the presidential retreat in Maryland's Catoctin mountains. Saudi Arabia, United Arab Emirates, Oman and Bahrain all sent lower-level but still influential representatives. The most notable absence was that of Saudi King Salman. On Sunday, Saudi Arabia announced that the king was skipping the summit, two days after the White House said he was coming.

Crown Prince Mohammed bin Nayef and Deputy Crown Prince Mohammed bin Salman were representing Saudi Arabia instead. The White House and Saudi officials insisted the king was not snubbing the U.S. president.

In Obama's remarks and the joint statement, the tone was conciliatory and positive, expressing commitments that they would work together on shared interests in the region, including efforts to combat Islamic State terrorism and continuing instability in Syria, Iraq, and Libya. Details of how they would do that, and which of the several conflicts raging across the Middle East, however, were few.

"We are still going to face a range of threats across the region," declared Obama. "We are going to work together to address these threats." He noted  they agreed Syrian President Bashar Assad had no future in Syria. Despite differences over how they would support Assad's opponents at the outset, the two sides agreed that they could cooperate to "ultimately destroy ISIL/DAESH in Syria," and warned "against the influence of other extremist groups, such as Al-Nusrah, that represent a danger to the Syrian people, to the region and to the international community."

The White House also welcomed the five-day cease fire in Saudi Arabia's bombing campaign of the Houthi rebels in Yemen, which along with the militants, has killed some 800 Yemeni civilians, according to the U.N. They also "strongly affirmed," with the partners, "the necessity of resolving the Israeli-Palestinian conflict on the basis of a just, lasting, comprehensive peace agreement that results in an independent and contiguous Palestinian state living side-by-side in peace and security with Israel."

With what seemed a nod to critics who say Obama has not pressured the Gulf leaders enough on human rights issues -- Saudi Arabia, for example, has been accused of numerous abuses, including the flogging of a political blogger, who still remains in prison -- earlier this year, Obama told reporters, that "true and lasting cooperation" includes a strong civil society, representative institutions and minority rights. He pledged the U.S. will help to expand economic and educational opportunities for young people, too.

For his part, Saudi Foreign Minister Adel al-Jubeir called Thursday a productive day. He said the Arab leaders were "assured that the objective is to deny Iran the ability to obtain a nuclear weapon," and that all pathways to such a weapon would be cut off. He added that it was too early to know if a final nuclear agreement would be acceptable, saying, "We don't know if the Iranians will accept the terms they need to accept."

As the leaders gathered, an Iranian naval patrol boat fired on a Singapore-flagged commercial ship in the Persian Gulf. A U.S. official said it was an apparent attempt to disable the ship over a financial dispute involving damage to an Iranian oil platform.

The incident took place a bit south of the island of Abu Musa just inside the Gulf, according to the U.S. official, who was not authorized to discuss details by name. The White House said no Americans were involved in the incident.

The Associated Press contributed to this report.