As Iran retaliates, largest US military base in Middle East hit by ballistic missile, Qatar says

President Donald Trump expressed optimism about the U.S.-Israeli attack on Iran saying it is going "very well," speaking to ABC News by phone.

Asked about how long it will last, Trump said, "As long as we wanted to, actually. But it’s done such damage already. It’s like — they are incapacitated, essentially -- as long as we wanted to."

Asked about Iranian leadership and whether the U.S. believes they were killed in strikes, Trump said, "A lot of it is, yeah. But we don’t know all, but a lot of it is. Was a very powerful strike."

Asked about the next leadership and if a leader has been identified, Trump said "Yes. We have a very good idea."

-ABC News' Jonathan Karl

U.S. Department of State Consular Affairs is urging Americans around the world, especially in the Middle East, to "exercise increased caution" and "follow the guidance in the latest security alerts issued by the nearest U.S. embassy or consulate."

Travelers "may experience travel disruptions due to periodic airspace closures," the department said.

Travelers were also encouraged to join the Smart Traveler Enrollment Program (STEP) "to receive the latest security alerts and follow the 'U.S. Department of State - Security Updates for U.S. Citizens' channel on WhatsApp" to receive travel alerts and updates, the department urged.

The White House is working to arrange full Senate and House member briefings this week on the Iran strikes, according to an administration official.

-ABC News' Selina Wang

President Donald Trump spoke with the leaders of Saudi Arabia, Qatar, the United Arab Emirates, and NATO Secretary General Mark Rutte, White House press secretary Karoline Leavitt said in a post on X on Saturday.

She did not offer any details on what was discussed.