Saudi Arabia's King Salman has designated his crown prince to attend a Gulf Arab summit with US President Barack Obama, the state news agency SPA reported on Sunday.

Foreign Minister Adel al-Jubeir announced that Crown Prince Mohammed bin Nayef would head the delegation representing the world's top oil exporter at the talks, which US sources say will focus on military cooperation.

A preliminary deal between Iran and world powers on Tehran's nuclear programme and the crises in Syria and Yemen are also likely to be discussed.

The summit, due to take place on Tuesday in Washington DC and then in Camp David, Maryland, coincides with the start of a five-day humanitarian truce in Yemen, proposed by Saudi Arabia and agreed to by the Houthi rebels it is fighting there.

Jubeir said Deputy Crown Prince and Defence Minister Mohammed bin Salman would also attend the summit for Saudi Arabia.

A US source said last week that Obama was expected to make a renewed US push at the summit to help Gulf allies create a region-wide defence system to guard against Iranian missiles as he seeks to allay their anxieties over the nuclear deal with Tehran.

The offer could be accompanied by enhanced security commitments, new arms sales and more joint military exercises, US officials say, as Obama tries to reassure Gulf Arab countries that Washington is not abandoning them.