US Secretary of State John Kerry met Saudi Arabia's King Salman in Jeddah on Sunday to discuss the fragile truce in Syria, before broader talks with Russia, Iran and other countries in Vienna on Tuesday.

Kerry has said he hopes to strengthen a "cessation of hostilities" agreement between Syrian government forces and rebels, which has been undermined by fighting in some areas, and to increase humanitarian aid deliveries to besieged areas.

On Friday, he said the meetings with the king and the Saudi interior and defence ministers - the two most senior princes - would try "to make sure that we can get this cessation better footed and, frankly, better observed and implemented throughout the country."

On Tuesday the US and Russia will co-chair a meeting of the International Syria Support Group, which includes Arab League and European Union countries as well as Turkey, Iran and China. – Reuters