US President Donald Trump spoke separately on Friday with Saudi Arabia's Crown Prince Mohammed Salman, United Arab Emirates Crown Prince Sheikh Mohammed bin Zayed al-Nahyan, and Qatar's Emir Sheikh Tamim Hamad al-Thani, the White House said in a statement.

Trump told them that unity among Washington's Arab partners was essential to promoting regional stability and countering the threat of Iran, the statement said.

"The president also emphasised that all countries must follow through on commitments from the Riyadh Summit to defeat terrorism, cut off funding for terrorist groups, and combat extremist ideology," it said.

Trump also spoke to Qatar's al-Thani on Thursday.

Trump told a news conference on Thursday that he would be willing to step in and mediate a dispute among the US-allied Arab states and Qatar, and said he thought a deal could come quickly.

Saudi Arabia, the UAE, Egypt and Bahrain cut diplomatic and trade links with Qatar on June 5, suspending air and shipping routes with the world's biggest exporter of liquefied natural gas, which is home to the region's biggest US military base.

The nations say Doha supports regional foe Iran and Islamists, charges Qatar's leaders deny.

- Reuters