Kerry in Riyadh ahead of potential showdown with Moscow

US Secretary of State John Kerry held talks in Saudi Arabia on Sunday to secure its support ahead of a potential showdown with Russia at talks on the Syrian conflict.

After his Saudi meetings, Kerry was due in Vienna which this week will host the international contact groups engaged in efforts to halt fighting in Syria and Libya.

Riyadh is the key backer of rebels fighting to overthrow Syria's President Bashar al-Assad, and Kerry is keen to keep the opposition on board with a shaky ceasefire in force since February.

Saudi allies Egypt and the United Arab Emirates are also major supporters of the administration in eastern Libya which is withholding its support from a UN-backed unity government in Tripoli.

Kerry met Saudi Arabia's King Salman and Crown Prince Mohammed bin Nayef at the royal court in a palace in Jeddah.

"I want to thank you for the many things that Saudi Arabia is working on with us to great effect," he told King Salman as the pair sat down, before reporters were ushered out.

"On Syria, the secretary provided an update of the situation on the ground following last week's reaffirmation of the cessation of hostilities," a US spokesman said.

"The secretary also gave an update on Libya," he said.

In talks with his Saudi counterpart Adel al-Jubeir, Kerry discussed "regional issues... mainly developments in Syria," the official Saudi Press Agency reported.

The monarch discussed "aspects of cooperation between the two countries and developments in the region and efforts in that regards," SPA reported.

Kerry also discussed cooperation in "fighting terrorism" with the Crown Prince, who is also interior minister.

Bin Nayef had orchestrated the kingdom's crackdown on al-Qaeda, which launched a wave of attacks on foreigners and government targets between 2003 and 2006.

After his talks in Vienna, Kerry will fly on to Brussels on Wednesday for a NATO foreign ministers' meeting and talks on the full range of challenges facing the Western allies

Focus on Libya security

After his talks in Vienna, Kerry will fly on to Brussels on Wednesday for a NATO foreign ministers' meeting and talks on the full range of challenges facing the Western allies.

State Department spokesman John Kirby said Kerry and Italian Foreign Minister Paolo Gentiloni will jointly host the Libya conflict meeting on Monday.

Participants will "discuss international support for the new Government of National Accord, with a focus on security," according to US officials.

The unity government was formed after months of negotiation by UN mediators in a bid to end the chaos of rival administrations in the east and west of Libya that has undermined the fight against the Islamic State group.

It has slowly asserted its authority in Tripoli since late March, taking over key institutions such as the central bank and the National Oil Corporation, but it still faces a rival administration in the east.

Officials say the fledgling regime is drawing up a list of requests for Western partners to assist its forces with arms, training and intelligence.

After the Libya meeting, Kerry and Russian Foreign Minister Sergei Lavrov will lead a meeting of the 17-nation International Syria Support Group.

The State Department's Kirby said last week the goal is to "ensure humanitarian access throughout the country, and to expedite a negotiated political transition."

The ISSG, chaired by Kerry and Lavrov, is pushing Syrian Assad's regime and a coalition of opposition groups to respect the fragile three-month-old ceasefire.

Officials hope next week's meeting will inject new life into the peace process and - if the ceasefire holds - secure talks on forming a unity government.

Syrian pro-government newspaper al-Watan reported on Sunday that peace talks might resume on 23 May, citing sources it did not identify.

On the ground, clashes between rival Islamist rebel factions near Damascus since late last month has killed more than 300 fighters, the Syrian Observatory for Human Rights monitor said on Sunday.