Iran 'spearhead of global terrorism', says Saudi King Salman

Saudi Arabia's King Salman has accused rival Iran of exporting extremist movements to the world, during a speech to Muslim and Arab leaders in Riyadh.

The address preceeded Donald Trump's first foreign speech as US leader, and Salman echoed many of the concerns the president raised about Iran and extremism.

Like Trump, Salman lumped the two together, accusing Iran of being the benefactor of instability and a promoter of terrorism in the region.

"The Iranian regime has been the spearhead of global terrorism since the [1979] Khomeini revolution," King Salman said.

"We did not know terrorism and extremism until the Khomeini revolution reared its head," he said.

Saudi Arabia was also determined to "eliminate the Islamic State group", the king said the king.

The United States and Saudi Arabia on Saturday announced an arms deal worth almost $110 billion, described as the largest in US history.

US Secretary of State Rex Tillerson said the deal was aimed at countering "malign Iranian influence".

Donald Trump later called for the "isolation of Iran", and spoke bitterly about Tehran's support for militant group Hizballah.

Agencies contributed to this story.