US President Donald Trump spoke with Saudi Arabia's King Salman amid the Arab world's biggest diplomatic crisis in years over Qatar's alleged support to extremists.
The two leaders spoke by phone after Saudi Arabia and its regional allies severed diplomatic ties with Qatar accusing the tiny Gulf nation of funding Islamist groups.
"The two leaders discussed the critical goals of preventing the financing of terrorist organisations and eliminating the promotion of extremism by any nation in the region," the White House said in a statement.
During the phone call, Trump underscored that a united Gulf Cooperation Council is critical to defeating terrorism and promoting regional stability, the White House said.
The Gulf Cooperation Council is a regional bloc comprising Saudi Arabia, Qatar, Kuwait, Bahrain, the UAE and Oman.
Saudi Arabia, the UAE, Bahrain, Egypt, Yemen and the Maldives have severed ties with Qatar blaming it for "financing, adopting and sheltering extremists" and supporting terrorist groups ranging from the Muslim Brotherhood and the Islamic State to the Iran-backed Houthi rebels.
Qatar has denied the allegations, in the biggest diplomatic crisis to have hit the region in years.
Earlier in a tweet, Trump signalled support for the effort to isolate Qatar, despite the country being home to the largest American airbase in the Middle East.
"During my recent trip to the Middle East I stated that there can no longer be funding of Radical Ideology. Leaders pointed to Qatar -- look!" Trump tweeted.
"So good to see the Saudi Arabia visit with the King and 50 countries already paying off. They said they would take a hard line on funding, extremism, and all reference was pointing to Qatar," he said.
"Perhaps this will be the beginning of the end to the horror of terrorism!" Trump said.
White House Press Secretary Sean Spicer told reporters that the US continues to be in close communication with all the parties to resolve the issues and restore cooperation which is so important to regional security there.
"I think there is note that his message of toughness on terror finance and extremism is being heeded by countries in the region. But the US still wants to see this issue de-escalated and resolved immediately, keeping with the principles that the president laid out in terms of defeating terror financing and extremism," he said.
Spicer said Trump had a very, very constructive conversation with the Emir of Qatar during his visit in Riyadh.
"At that time, he was very heartened by the Emir's commitment to formally join the terrorist financing targeting centre and showing their commitment to this issue," he said.
At a separate briefing, State Department Spokesperson Heather Nauert said the US recognises that Qatar has made some great efforts to try to stop financing of terror groups, including prosecuting suspected financiers, freezing assets, and introducing stringent controls on its banking system there.
"However, let me make this clear: They have made progress, but they still have work to do. More work needs to be done," she said.
"I think our relationship with Qatar is one that's strong. It's one that we continue to cooperate with Qatar and other countries in the region in the fight against terrorism.
"Secretary of State Rex W Tillerson talked about this today," she added.
"He said every country in the region has their own obligations and they need to live up to terminate their support for terrorism and extremism however it manifests
itself anywhere in the world," she said.
Nauert praised Qatar for its role in fight against terrorism.
"The US and its coalition, we're grateful to the Qataris for their longstanding support of our presence there in that nation. They have helped to provide us with an enduring commitment to regional security. The Department of Defense has talked about this," she said.
"We have no plans to change our posture in Qatar and we would encourage all of our partners to try to work together to reduce tensions. That's something that the Secretary spoke to as well," Nauert said in response to a question.