President Barack Obama is beginning a visit to Saudi Arabia at a time of strained relations between the US and Gulf countries.
As well as meeting King Salman, he will sit with leaders from Gulf Cooperation Council (GCC) countries.
US Defence Secretary Ashton Carter is on the trip with him.
Mr Carter said they would be seeking help with military and naval operations to counter Iran’s “destabilising activities” in the region.
Later in the week, President Obama will travel to the UK and Germany.
Analysis: Frank Gardner, BBC Security Correspondent
Behind the red carpet welcome and the official press briefings there are signs of real strain in the 71-year old US-Saudi strategic partnership.
Whatever polite words the Saudis may utter in public, for them, President Obama is the living embodiment of their disappointment with the current US administration.
The White House too has its own frustrations with Riyadh, some of which have spilled over into public comments.
In short, the relationship is not broken – Saudi Arabia and the US still need each other – but their alliance is probably under more strain now than at any time since the 1973 Arab-Israeli war.
The US support for the lifting of sanctions against Iran has damaged relations with Saudi Arabia, Iran’s biggest rival in the region.
And a bill that is being considered in the US at the moment could potentially allow American citizens to sue Saudi Arabia over the 9/11 attacks.
The GCC includes Saudi Arabia, Bahrain, the United Arab Emirates, Kuwait, Qatar and Oman.