US President Donald Trump declined an appeal by Saudi Crown Prince Mohammed bin Salman for American military strikes on Yemen’s Iran-backed Houthi movement, according to reports published Friday.

Axios, citing two US officials, said Mohammed bin Salman spoke to President Trump twice on Thursday as Houthi forces pushed along Yemen’s Red Sea coast. The Saudi leader reportedly sought US intervention as the group moved nearer to the Bab el Mandeb Strait, the narrow waterway linking the Red Sea and the Gulf of Aden.

The passage is a major route for international shipping and Saudi oil exports. Concern over its security has increased after the Houthis captured the strategic coastal city of Mokha.

Despite the decision not to directly strike Yemen, the United States is increasing its support for Saudi Arabia. More than 100 US military advisers are in the kingdom, providing intelligence and target-selection assistance to Saudi operations, CNN reported, with one official putting the overall US deployment connected to the effort at roughly 200 personnel.

The support does not include US participation in airstrikes, refueling for Saudi warplanes or other direct operational roles, according to CNN. US personnel are instead helping Saudi forces use real-time battlefield and geospatial intelligence.

Admiral Brad Cooper, head of US Central Command, travelled to Saudi Arabia on Thursday for urgent coordination talks.

A senior US administration official said Washington’s priority is protecting freedom of navigation in the Red Sea while leaving the wider confrontation to regional partners. “The United States is focused on protecting our core national security interests,” the official said.