US President Barack Obama will visit King Salman and the Saudi royal court in Riyadh next week in a bid to mend increasingly frayed ties between the allies.

Before his election, Obama famously dismissed Saudi Arabia as America's "so-called ally" and relations have remained tense through both his two terms.

Although Wednesday's visit will be his fourth to the kingdom, the Saudis were dismayed by his outreach to Iran and support for some Arab Spring revolts.

The countries work together in the fight against the Islamic State group but the kingdom feels Obama could have been tougher on Syria's Bashar al-Assad.

And eyebrows were raised last year when King Salman decided not to join a summit of Gulf leaders hosted by Obama at his Camp David country residence.

But senior Obama adviser Rob Malley said that since then, there has been real progress in the relationship.

"On the security front, over the last 12 months, there have been countless meetings at all levels," he said.

After Wednesday's royal audience, Obama and Salman will meet leaders of the Gulf Cooperation Council, the powerful Saudi-dominated regional grouping.

"There has been much deeper cooperation between us and the GCC," Malley argued, citing efforts to stabilize regional conflicts in Libya and Yemen.

"There is still much more work to be done. But in Yemen, the situation is far better than it was a year ago," he said, citing a ceasefire that began Sunday.

"Likewise in Syria, there is a fragile cessation of hostilities but it has held so far for seven weeks," he said, admitting: "Much more needs to be done."

Obama will leave Riyadh on Thursday night and fly on to Britain and then to Germany.
Source: AFP