US Secretary of State Rex Tillerson called Sunday for a "lowering of rhetoric" between Qatar and a four-nation group led by Saudi Arabia after Doha denounced their sweeping list of demands.
Saudi Arabia, Bahrain, the United Arab Emirates and Egypt want Qatar to meet their 13-point ultimatum -- ostensibly aimed at fighting extremism and terrorism -- in return for an end to a nearly three-week-old diplomatic and trade "blockade" of the emirate.
But Qatar on Saturday rejected the demands as unrealistic, calling the blockade "illegal." Its ally Turkey joined in, with President Recep Tayyip Erdogan saying on Sunday that the ultimatum was "against international law."
Tillerson attempted to soothe fraying tempers in a statement Sunday, following days of telephone diplomacy with Riyadh and Doha.
The diplomatic tiff, which some observers believe President Donald Trump might have encouraged through his full-throated support for Saudi Arabia during a recent visit, could threaten the future of a huge US air base in Qatar.
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"While some of the elements will be very difficult for Qatar to meet, there are significant areas which provide a basis for ongoing dialogue leading to resolution," Tillerson said, urging the countries to "sit together and continue this conversation."
"We believe our allies and partners are stronger when they are working together towards one goal which we all agree is stopping terrorism and countering extremism," he said. "A lowering of rhetoric would also help ease the tension."
Qatar insists that the moves against it have more to do with long-standing differences than with the fight against extremism.
"It is about limiting Qatar's sovereignty and outsourcing our foreign policy," said Sheikh Saif bin Ahmed Al-Thani, a government spokesman.
The four Arab governments delivered the ultimatum on Thursday. The document has been widely leaked and the demands are sweeping.
They include the closure of Al-Jazeera television, which neighboring countries accuse of fomenting regional strife; and a call for Doha to cut ties to groups including the Muslim Brotherhood, the Islamic State organization, Al-Qaeda and Lebanon's Iran-backed Hezbollah movement.
Qatar has also been asked to hand over opposition figures wanted by the four countries, to downgrade diplomatic ties with Iran, and to shut a Turkish military base.