A State Department spokesperson questioned whether the crisis is a result of "long simmering grievances"
The US State Department says it is "mystified" that Gulf states have not formally detailed their reasons behind their continued embargo of Qatar.
It is now more than two weeks since countries including Saudi Arabia, the United Arab Emirates and Bahrain cut off diplomatic ties with the state.
The blockade has had many major impacts for Qatar, including essential trade being cut off and many flights suspended.
A number of reasons have been cited for the blockade - including Qatar's relations with Iran; Arab states' concerns over the Doha-based Al Jazeera news station; and the Qatari state's alleged support of terrorist and extremist groups.
The Qatari Foreign Affairs Minister Sheikh Mohammed bin Abdulrahman Al-Thani, however, has insisted they have not received any formal accusations or demands from the other countries.
In a meeting with journalists earlier this week, he said: "We can not expect an end to the crisis - solutions are not yet developed, and the countries [that have] besieged Qatar have not provided any clear reasons for the steps they have taken."
US officials have appeared to shift their response to the diplomatic crisis. Although President Donald Trump originally praised the Gulf states for the blockade, the administration has since been involved in efforts to encourage the countries involved to enter talks to resolve the crisis.
So good to see the Saudi Arabia visit with the King and 50 countries already paying off. They said they would take a hard line on funding...— Donald J. Trump (@realDonaldTrump) June 6, 2017
...extremism, and all reference was pointing to Qatar. Perhaps this will be the beginning of the end to the horror of terrorism!— Donald J. Trump (@realDonaldTrump) June 6, 2017
US Secretary of State Rex Tillerson is said to have had more than 20 phone calls and meetings with officials from the Gulf states involved.
In a press briefing Tuesday, US State Department spokesperson Heather Nauert explained: "Now that it’s been more than two weeks since the embargo started, we are mystified that the Gulf states have not released to the public, nor to the Qataris, the details about the claims that they are making toward Qatar.
"The more that 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 [Gulf Cooperation Council] countries?"
She also stated that her department believes the situation can be "resolved peacefully among the parties without the United States having to step in in some sort of formal mediation role".
The remarks were welcomed by Qatar, with an official reiterating the country's "support of resolving the crisis through a civilised dialogue".