Washington — President Obama will play diplomat this coming week during a global trip, with emphasis on one special relationship and an increasingly awkward one.

The trip will provide a reminder that the United Kingdom remains America’s closest ally. It also will highlight Germany’s standing as a European power. But it also will provide the latest illustration of how another longtime ally, Saudi Arabia, continues to drift from Washington’s orbit on key issues.

On such issues as the fight against Islamic State and dealing with Iran, there are many strains to the U.S.-Saudi relationship.

White House officials have been critical of Saudi leaders and the heads of other Sunni Muslim countries, urging them to do more to confront Islamic State.

“We do hope that we and the (Gulf Cooperation Council) will be able to do more in the fight against the terrorist threat and work in even greater partnership on that,” said Robert Malley, a senior adviser to the president for countering Islamic State.

The Gulf Cooperation Council includes Saudi Arabia and the Persian Gulf states of Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates.

Sen. Tim Kaine, D-Va., a member of the House Foreign Relations and Armed Services committees, said U.S. officials “want them to be all in on ISIS” but instead “we don’t see an urgency on their part.”

The frustration cuts both ways. Saudi officials and their Sunni allies wonder why Obama has taken a more hands-off approach to the Middle East than many of his predecessors.

Obama heads to Saudi Arabia for a private meeting Wednesday with the Saudi leader, King Salman bin Abdulaziz Al Saud.

Obama, Salman and the other GCC leaders will then hold three distinct sessions. There will be one on Islamic State and al-Qaida, and another on general regional stability.

But there also will be one on a more touchy issue for the Sunni leaders: “Iran and regional security and our efforts to prevent destabilizing actions across the region,” said Ben Rhodes, deputy White House national security adviser.

There will be disagreements and calls to strengthen joint efforts on all three issues. But many lawmakers agree that Obama will hear one overarching message from the Sunni leaders about fighting Islamic State in Syria, and a list of other Middle East security matters.