Donald Trump sides with Saudi Arabia amid deepening Middle East crisis

US President Donald Trump has called the king of Saudi Arabia to stress the critical need for a united Gulf amid a deepening diplomatic crisis with Qatar over its alleged support for extremists.

A White House statement said the two leaders discussed the "critical goals" of preventing the financing of "terrorist organisations" in any nation in the region.

Earlier on Tuesday Mr Trump had appeared to endorse the accusation that the oil-rich nation is funding terrorist groups - a charge strongly denied by the Persian Golf nation.

Last month the president hailed his visit to Saudi Arabia, where he met with dozens of Arab and Muslim leaders - including Qatar's Emir.

At the time he described their relationship as "extremely good".

However during a series of tweets on Tuesday he appeared to slam Qatar by saying his visit was "already paying off" as funding of "Radical Ideology" can no longer be tolerated.

Donald Trump held a bilateral meeting with Qatar's Emir Sheikh Tamim Bin Hamad Al-Thani last month. Credit: AP

He then wrote: "They said they would take a hard line on funding extremism, and all reference was pointing to Qatar.

"Perhaps this will be the beginning of the end to the horror of terrorism!"

The president's condemnation of Qatar put Washington directly into the crisis that has put the small country against Saudi Arabia, Bahrain, Egypt, Jordan and the United Arab Emirates.

Qatari foreign minister Sheik Mohammed bin Abdulrahman bin Jassim Al-Thani, pictured earlier this year. Credit: AP

Those countries said they were cutting diplomatic ties with Qatar in a move that led airlines to suspend flights, Qatari ships being banned from ports and residents to start stockpiling food.

Its neighbours have long accused the country of tolerating, or even encouraging support for extremist groups, including al-Qaida's branch in Syria - formerly called the Nusra Front - and the Muslim Brotherhood in Egypt.

Qatar is currently home to a major US military base and it is unclear how Mr Trump's diplomatic fallout might affect their presence in the country.

Some 10,000 American troops are currently based there.