“They didn’t expect anything, but they’re still disappointed,” said Hussein Ibish, a senior resident scholar at the Arab Gulf States Institute, a Washington-based think tank.

On Wednesday, President Trump added to the concern by telling a news conference at the Group of 7 summit in France that Iran should be able to have some ballistic missiles because neighboring countries have them too.

Mr. Trump’s comments were in stark contrast with comments by Secretary of State Marco Rubio in the early days of the war that the United States was attacking Iran to “eliminate the threat of Iran’s short-range ballistic missiles.”

“They’re not going to have these ballistic missiles and they’re not going to have drones to threaten us,” Mr. Rubio said at the time. The “objective of the mission,” he added, was to “deny them the ability to use ballistic missiles to threaten their neighbors, to threaten our bases, to threaten our presence in the region.”

Government officials from Kuwait, the United Arab Emirates, Bahrain, Saudi Arabia, and Qatar did not immediately reply to requests for comment.

Bader Al-Saif, an assistant professor of history at Kuwait University, said excluding Iran’s missiles and drones from the agreement showed that the United States “doesn’t have our best interests in mind.”

Mr. al-Saif said he has no doubt that Iran was already rebuilding its missile and drone capacities and that it would use the financial windfall it gets from the deal to acquire more of the weaponry. The agreement, which U.S. and Iranian officials have called a memorandum of understanding, says the Department of Treasury will issue waivers for the export of Iranian crude oil, petroleum products and derivatives.

Without limits on Iran’s missile and drone programs, Gulf countries could resort to boosting their investment in air defense technology and increasing diplomacy with the Islamic Republic, according to Marc Sievers, a former senior American diplomat who served in several countries in the Middle East.

“Those are the main options on the table,” he said.

Mr. Ibish said Gulf governments would likely turn to Ukraine and South Korea for advice on countering missiles and drones.

Officials in the region, he added, were increasingly wondering whether they can rely on the United States as a security guarantor, especially after the Trump administration did not heed their warnings about going to war with Iran.

“The question is how do they see Washington fitting into their national security doctrine,” he said, referring to the Gulf countries. He said that they were slowly exploring the idea of “really moving on from reliance on the United States, if it doesn’t do anything to reassure them in the next 12 months.”

Finding a replacement solution, however, will take a decade or two, Mr. Ibish said, adding that the Gulf countries would have to stay close to the United States in the meantime.

Ismaeel Naar contributed reporting from Dubai.