The US State Department on Tuesday questioned the motives of Saudi Arabia and the United Arab Emirates (UAE) for their boycott of Doha, saying it was "mystified" as Gulf Arab states had not released to the public or Qatar details of the grievances that prompted their boycott of the country.
The UAE, which along with Saudi Arabia, Egypt and Bahrain imposed the measures to isolate Qatar, accusing it of supporting terrorism.
The State Department said the more time goes by, "the more doubt is raised about the actions taken by Saudi Arabia and the UAE."
"At this point, we are left with one simple question: Were the actions really about their concerns regarding Qatar's alleged support for terrorism or were they about the long-simmering grievances between and among the GCC countries," State Department spokeswoman Heather Nauert said, referring to the six-nation Gulf Cooperation Council.
Qatar's ambassador to the United States, Meshal Hamad al-Thani, welcomed the State Department's statement, tweeting: "We are confident in the ability of the US to resolve this crisis".
While the State Department sought to remain neutral, US President Donald Trump has accused Qatar of being a "high level" sponsor of terrorism.
But Qatar has denied accusations by its neighbours that it funds terrorism, foments regional instability or has cosied up to their enemy, Iran.
There was no immediate comment from Riyadh or Abu Dhabi.
Ending the dispute
The fact the State Department bluntly questioned Riyadh and Abu Dhabi's actions in public suggests Washington was keen for the parties to end the dispute.
"We've just said to the parties involved: Let's finish this. Let's get this going," Nauert said.
Qatar hosts a vital US military base, Al Udeid, to which more than 11,000 US and coalition forces are deployed or assigned, and from which more than 100 aircraft operate.
The Pentagon has said the boycott was hindering US ability to plan for long-term operations in the region.
Al Udeid is where the command for the anti-Daesh air campaign takes place.
Saudi Arabia, the United Arab Emirates, and Qatar are key American allies.
The State Department, headed by Secretary of State Rex Tillerson, was encouraging "all sides to de-escalate tensions and engage in constructive dialogue," Nauert said.
A US official said Washington is urging Qatar to take steps to defuse the crisis, including signing on to proposals being drawn up the Treasury Department to strengthen controls against the financing of militant groups.
But this official and a second US official said it was inaccurate to single Qatar out, and that the Saudis, Emiratis, and other Gulf states face similar challenges in countering terrorist financing.
Qatar's foreign minister, who is expected to travel to Washington next week, said Doha would not negotiate with its neighbours to resolve the Gulf dispute unless they first lift the trade and travel boycott they imposed two weeks ago.
He added that Doha still believed a solution was possible.
The first US official said the dispute is driven more by economic rivalries, historical tensions and the personal dynamics of Gulf leaders than by the specific demands the Saudis and Emiratis are making on Qatar.
Nauert said Tillerson had three phone calls and two in-person meetings with the Saudi foreign minister. Tillerson also spoke by phone three times with Qatar's foreign minister and with the Qatari emir.
The UAE's ambassador to the US said last week a list of demands for Qatar was being compiled and would soon be handed to the US.
He said they would broadly address support for terrorism, meddling in the internal affairs of these countries and attacks through Qatari-owned media platforms.
Meanwhile, Qatar's attorney general said on Tuesday his country had evidence that the hacking of Qatar's state news agency was linked to countries that have severed ties with Doha.