President Obama on Thursday offered Saudi Arabia and smaller Arab states new support to defend against potential missile strikes, maritime threats and cyberattacks from Iran, calling his commitment to their security “ironclad” in an effort to allay fears that a nuclear accord will empower Tehran, their main rival in the Middle East.

But in a daylong meeting here, Mr. Obama stopped short of offering a formal defense pact that would obligate the United States to come to the nations’ aid if they were attacked. Instead, he tried to reassure them that he was serious about bolstering their security and willing to help them counter Iran.

“I am reaffirming our ironclad commitment to the security of our gulf partners,” Mr. Obama said at a news conference at the wooded presidential retreat here after seeing off the leaders of the Gulf Cooperation Council, who had attended a day of private meetings here. […]