U.S. President Barack Obama has met with King Salman bin Abdulaziz in the Saudi capital Riyadh.

The two leaders discussed the conflicts in Syria, Yemen and Iraq. Obama said he welcomed Saudi Arabia’s role in the coalition against the Islamic State militant group.

This is his fourth visit to the oil-rich Gulf nation since taking office. The kingdom is seen as one of Washington’s most strategic allies in the Middle East, but bilateral relations were strained by the nuclear deal reached with Iran last year.

Obama is also expected to attend a summit with the six Gulf Cooperation Council countries during his visit.