Efforts to end a two-week-old crisis in the Persian Gulf shifted to the US, with Secretary of State Rex Tillerson canceling a trip to Mexico to try to end a Saudi-led coalition’s isolation of Qatar.

The foreign minister of the United Arab Emirates, which is part of the coalition, affirmed a need for a strong Western role in resolving the dispute, telling the Guardian newspaper in the U.K. that any agreement would have to be overseen by "Western allies."

Kuwait and Turkey have been trying to mediate the dispute, which erupted over Qatar’s ties to Iran and Islamist groups, but their attempts stalled as Qatar awaited a list of demands from Saudi Arabia and the UAE Tillerson’s formal role in trying to broker a deal emerged over the weekend when the State Department said he would skip a meeting of the Organization of American States in Cancun on Monday to focus on the Gulf dispute.

"The Secretary of State will continue his efforts to de-escalate tensions in the Middle East region through in-person meetings and phone conversations with Gulf and regional leaders," the department said in a statement Friday. It said Tillerson has "made more than a dozen phone calls and participated in several in-person meetings."

Tillerson assumes the role of Gulf mediator after having forged ties with regional leaders during his years as chief executive officer of Exxon Mobil Corp. Shortly after Saudi Arabia, the UAE, Bahrain and Egypt severed diplomatic, transport and trade links, President Donald Trump had offered to have him try to broker a solution.

Tillerson has already met with top officials from Qatar, Saudi Arabia and the UAE in recent days. Qatar denies the coalitioin’s allegations that it supports terrorist groups and Iran, and has accused Saudi Arabia of seeking to dominate smaller states within the energy-rich region.

A Gulf official with direct knowledge of the matter told Bloomberg on Thursday that Saudi Arabia and the UAE were expected to relay to mediators a list of demands soon. So far, Qatar hasn’t received any demands from Gulf nations, Foreign Minister Mohammed Al Thani told Qatar TV, calling the delay "evidence of the fragility of the basis of the actions against Qatar."

The UAE minister of state for foreign affairs, Anwar Gargash, said an agreement would require Qatar to stop supporting Islamist groups such as the Muslim Brotherhood, Hamas and al-Qaeda -- a charge it denies.

"There is zero trust, but we need a monitoring system and we need our Western friends to play a role in this," Gargash told the Guardian.

The flareup in the Gulf puts the US in a difficult position because it is allied with nations on both sides of the dispute. Moreover, Qatar hosts the regional headquarters for the US Central Command, which includes a state-of-the-art air base the Pentagon depends on to target Islamic State.

Tillerson’s efforts have been hindered by mixed messages from the administration. The secretary of state initially called on Saudi Arabia to ease what he called "the blockade" on June 9, only to have Trump, at a White House news conference hours later, say the move had been the right one.

"The nation of Qatar, unfortunately, has historically been a funder of terrorism at a very high level," Trump said in a speech at the White House. "We ask Qatar, and other nations in the region to do more and do it faster."

The Trump administration’s position was clouded further this week when the Defense Department announced that Qatar would sign a $12 billion deal to buy as many as 36 F-15 jets from the US. (Bloomberg)