US officials and experts agree that the rapprochement between Saudi Arabia and Iran, with Chinese mediation and sponsorship, constituted a significant diplomatic breakthrough.
Some observers believe the agreement may rearrange alliances and rivalries in the region, leaving the United States on the sidelines, at least temporarily.
The US, which has been the central actor in the Middle East, now finds itself on the sidelines during a moment of significant change, whereas China, which played only a secondary role in the region, has suddenly transformed itself into the new power player.
Publicly, the White House welcomed the restoration of diplomatic relations between Saudi Arabia and Iran and did not express an explicit "concern" about Beijing's role.
However, President Joe Biden's aides suggested too much was being made of the breakthrough, scoffing at suggestions that it indicated any erosion in US influence in the region, according to the New York Times.
The Washington Post quoted a senior administration official briefed on the talks between Tehran and Riyadh, saying that the United States was updated on the negotiations from the beginning.
He indicated that the Saudis had made it clear to US officials that they were interested in restoring diplomatic relations with Iran.
The Saudis also made it clear that they were unwilling to make such a deal without solid guarantees from the Iranians that attacks against them would stop and that they would reduce military support for the Houthis.
The official emphasized that Oman also played an important role, prompting Biden to contact the Sultan this week.
Analysts said it remained unclear how far the rapprochement between Saudi Arabia and Iran would go. After decades of sometimes violent competition for leadership in the Middle East and the broader Islamic world, reopening embassies closed in 2016 represents only a first step.
It is conceivable that this new agreement to exchange ambassadors may not even be carried out in the end, given that it was put on a cautious two-month timetable to work out details.
The key to the agreement was a commitment by Iran to stop further attacks on Saudi Arabia and curtail support for militant groups that have targeted the kingdom.
Despite this, US officials expressed doubts that Iran would live up to its new commitments. They believe that Tehran's turn to Beijing to mediate with the Saudis.
However, it increases China's presence in the region, and also reflects its quest to escape from the isolation imposed by Washington.
Biden administration officials say Iran is under pressure and suffering from deep economic distress because of American sanctions. But that does not mean China, one of the signatories to the original nuclear deal, wants Iran to have a nuclear weapon either.
If Beijing has new sway in Tehran, American officials hope it could use it to curb Iran's nuclear ambitions.
However, it is disconcerting for many veteran US policymakers to see China playing such an outsize role in a region, reflecting two types of approaches to the Saudi Iranian agreement.
Some condemned Biden's policies, blaming them for the decline in Washington's relations with its regional allies and its neglect of the opportunity to achieve a breakthrough in Arab relations with Israel. At the same time, others called for what can be practically achieved, despite suspicions concerning Iran's role.
Head of the Foundation for the Defense of Democracies Mark Dubowitz described the renewed Iranian-Saudi ties due to Chinese mediation as a "lose, lose, and lose for American interests."
Whereas the deputy director for research at the Project on Middle East Democracy, a Washington-based nonprofit group, Amy Hawthorne, said there was no way around it, saying: "this is a big deal."
"The United States could not have brokered such a deal with Iran since we have no relations. But in a larger sense, China's prestigious accomplishment vaults it into a new league diplomatically. It outshines anything the US has been able to achieve in the region since Biden came to office."
Matt Duss, a visiting scholar at the Carnegie Endowment for International Peace, said that anything that lowers the temperature between Iran and Saudi Arabia and reduces the possibility of conflict is a good thing.
"It is also a potentially encouraging sign that countries in the region can pursue such initiatives without requiring lots of goodies and guarantees from the US," Duss added.
Though reducing China's influence in the Middle East and other parts of the world remains a priority for the Biden administration, it is of "two minds" about the agreement, according to John Alterman, a Middle East scholar at the Center for Strategic and International Studies.
Alterman said: "It wants the Saudis to take increasing responsibility for their security, but it does not want Saudi Arabia freelancing and undermining US security strategies."