President Donald Trump is ramping up pressure on Qatar to stop what he calls a “high level” of financial support of terrorism, even as Secretary of State Rex Tillerson tries to calm the worst diplomatic crisis in the Persian Gulf in years.

Trump's demand that there be “no more funding” by Qatar for extremists groups contradicted the message delivered Friday by Tillerson, who had urged Qatar's neighbours to ease their blockade while calling for “calm and thoughtful dialogue.”

Only an hour later, Tillerson sat in the front row in the Rose Garden as Trump enthusiastically embraced the move by Saudi Arabia, Egypt and others to punish Qatar.

“The nation of Qatar, unfortunately, has historically been a funder of terrorism at a very high level,” Trump said, echoing an allegation the Saudi-led group has used to justify cutting diplomatic ties to the tiny gas-rich kingdom.

“We have to stop the funding of terrorism.” Despite Tillerson's plea for “no further escalation,” Trump's sharp comments were likely to further embolden Saudi Arabia and the others in their bid to isolate Qatar.

The State Department had said the U.S. learned only at the last minute about the Arab nations' plan to cut ties. But Trump said that he, Tillerson and military leaders had decided during Trump's trip to Saudi Arabia last month that a public rebuke was needed.

“The time had come to call on Qatar to end its funding they have to end that funding and its extremist ideology in terms of funding,” Trump said.

Though the president said others, too, were guilty of supporting terrorism, he said he would not name them.

In a day of mixed messages and chaotic diplomacy, Tillerson emphasised the economic, humanitarian and military damage he said the blockade was inflicting.

He said families were being separated, children removed from school and Qataris forced to deal with food shortages.

“We believe these are unintended consequences, especially during this Holy Month of Ramadan, but they can be addressed immediately,” he said.

Tillerson also said the blockade by Qatar's neighbours was “hindering U.S. military action in the region, and the campaign against ISIS,” using an acronym for the Islamic State group.

But at the Pentagon, a spokesman, Navy Capt. Jeff Davis, said only long-term military planning was affected. Davis said the diplomatic rift has not interrupted or curtailed operations at al-Udeid air base, a launching pad for U.S. military efforts in Iraq, Syria and Afghanistan.

Still, the Pentagon has been developing contingency plans in case there's any interruption, defence officials said.

Aircraft that fly out of Qatar — including fighter jets, drones and refuelling planes — can be relocated to a number of other bases in the region including in Iraq, Turkey, Kuwait and Bahrain and off aircraft carriers, the officials said.

There was no immediate reaction from Qatar, which hosts some 10,000 U.S. troops. The Qatari Embassy in Washington did not respond to a request for comment.

The escalating crisis in the Persian Gulf erupted this week when Saudi Arabia, the UAE, Egypt and Bahrain cut ties to Qatar, accusing the country of tolerating or even encouraging support for extremist groups, including al-Qaida's Syria branch. Qatar's neighbours have also criticised Qatar for allegedly supporting groups like the Muslim Brotherhood and Hamas.

“Qatar has a history of supporting groups that span the spectrum of political expression, from activism to violence,” Tillerson said.

He credited Qatar's emir with making progress in curbing financial support and expelling terrorists, but added, “He must do more, and he must do it more quickly.”

The spat has led to one of the worst Gulf crises in decades, with suspended flights and regional ports closed to Qatari ships. Increasing the pressure Friday, Qatar's neighbours put 12 organisations and 59 people on a terror sanctions list and described them as being associated with Qatar.

The kingdom called the allegations “baseless.” Tillerson, speaking at the State Department, said the U.S. would help support efforts to mediate the crisis, along with Kuwait another Gulf country that has stepped up to try to broker a resolution.

Urging all sides to avoid further escalation of the conflict, Tillerson said the elements were available to resolve it.