Trump's comments came as Washington joins intensifying global efforts to heal the worsening rift between the key Western Gulf allies, which has escalated into the region's worst diplomatic crisis in years.
Kamal Alam, a visiting fellow at diplomatic and defence think-tank RUSI, told Middle East Eye that a prolonged crisis in the Gulf could see Turkish military power in Qatar grow.
In an interview with BBC radio, UAE Ambassador to Russia Omar Saif Ghobash said Qatar had to choose between supporting extremism or supporting its neighbours.
The blockade is hindering U.S. military actions in the region and the campaign against the Islamic State group, Tillerson said, adding that it is also impairing USA business activities in the region and bringing about humanitarian consequences, Xinhua reporeted. "They said they would take a hard line on funding extremism, and all reference was pointing to Qatar", said Trump.
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"Our expectation is that these countries will immediately take steps to de-escalate the situation and put forth a good-faith effort to resolve their grievances they have with each other", said Tillerson.
It gave the example of a Saudi man, a resident of Doha with his Qatari wife and children, who had been unable to visit his sick mother hospitalised in Saudi Arabia because he would be blocked from returning to his family. "But the Saudi Islamic Arab coalition could fall apart and, maybe, if the situation continues we might see the first steps of replacing U.S. protection in Qatar for Turkish protection".
Still, the Pentagon has been developing contingency plans in case there's any interruption, defense officials said.
Tillerson also noted that the Gulf countries - all members of the Gulf Cooperation Council and all involved in the fight against ISIS - have to stay unified for the sake of that effort. "The most plausible theory at this stage is that this was more about Saudi and Emirati enforcement of gulf domination than the other explanations would suggest, and more enabled by Trump's implicit blessing of that bid".
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Referring to the conversations that he had with leaders of the Gulf countries, Tillerson said it is clear to him based that the elements of a solution are available.
Bahrain, Saudi Arabia, Egypt, the UAE and several other countries severed diplomatic and transport ties with Doha on Monday, accusing it of supporting Islamist militants and their arch-foe Iran - charges Qatar says are baseless. We believe these are unintended consequences, especially during this Holy Month of Ramadan, but they can be addressed immediately.
Some reports alleged that Russian hackers helped spark the crisis but Moscow has dismissed this as a "stale claim" with "zero evidence".
The rupture is based on the accusation that the Qatari government finances terrorist organisations, including the Islamic State, Al Qaida and the Muslim Brotherhood, an accusation that Qatar has denied.
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