WASHINGTON—The White House canceled plans for a summit this month between President Barack Obama and Persian Gulf monarchs in Riyadh because of splits between Washington's closest allies in the region, according to diplomats briefed on the decision.

The strains that scuttled the meeting with leaders of the Gulf Cooperation Council countries—Saudi Arabia, the United Arab Emirates, Qatar, Bahrain, Oman, and Kuwait—underscored the mounting challenges Washington faces in trying to contain the Middle East's spiraling political turmoil, these officials said.

Mr. Obama is still scheduled to meet face-to-face with Saudi Arabia's King Abdullah in Riyadh late next week at the end of a trip largely focused on Europe and the crisis in Ukraine.

The U.S. has worked to unify the GCC on security and economic issues in recent years, in particular on strategies to end Syria's civil war and to contain Iran's nuclear program.

But Saudi Arabia, the U.A.E. and Bahrain all withdrew their ambassadors from Qatar this month to protest the Arab country's regional policies, notably its support for the Muslim Brotherhood, an Islamist organization active in Syria, Libya and Egypt.