The Qataris have also gained ground in Washington. While Mr. Trump initially cheered the blockade, endorsing the Saudi allegation that Qatar supported terrorism, he later switched tracks. Last year, he welcomed Qatar’s emir in Washington and this month sent his daughter and senior adviser, Ivanka Trump, to a major conference in Doha.

But the antagonism toward Qatar has not softened in the Emirates, which has been a leader of the embargo and which still sees Qatar as dangerously close to the region’s Islamists. The distrust is reciprocated by Qatar, where officials have spoken of possibly reconciling with Saudi Arabia but not the Emirates, effectively splitting their alliance.

Concrete progress has been scarcest where the stakes are highest: between Saudi Arabia and Iran. But after years of heated statements and competing support for opposite sides in regional conflicts, officials from Pakistan and Iraq have stepped in as intermediaries for back-channel talks aimed at averting a wider conflict.

It remains unclear how far such talks will go in reducing tensions, especially since an official Saudi opening with Iran could infuriate Mr. Trump, who has tried to isolate and punish Iran.

“Washington would not look kindly upon a Saudi-Iranian channel at a time when the U.S. is trying to isolate Iran,” said Mr. Malley, the Obama administration official. “Not to fully trust the Trump administration is one thing. To openly defy it is another altogether, and Prince Mohammed is unlikely to do that.”

Saeed al-Batati and Shuaib Almosawa contributed reporting from Yemen.