Assad must step down or face 'military option': Saudi foreign minister

Syrian leader Bashar al-Assad must leave office or face being turfed out by force, Saudi Foreign Minister Adel al-Jubeir said Tuesday, warning of stepped up support for Syrian rebel groups.

Jubeir rejected Russian calls for an international coalition to help Assad fight the Islamic State (IS) group, and said the Syrian leader's best option would be to step down.

"There is no future for Assad in Syria, with all due respect to the Russians or anyone else," Jubeir told reporters in New York after meetings with Saudi Arabia's allies.

"There are two options for a settlement in Syria. One option is a political process where there would be a transitional council," he said, describing this as the "preferred option".

"The other option is a military option, which also would end with the removal of Bashar al-Assad from power," Jubeir warned.

"This could be a more lengthy process and a more destructive process, but the choice is entirely that of Bashar al-Assad."

Jubeir would not be drawn on specifics of what the military option would look like, but noted that Saudi Arabia is already supporting "moderate rebels" in their battle against Assad.

"Whatever we may or may not do we're not talking about," he said, adding: "There is a Free Syrian Army that is fighting against Bashar al-Assad. 

"There is a moderate Syrian opposition that is fighting against Bashar al-Assad and this opposition is getting support from a number of countries, and we expect that this support will continue and intensify."

US President Barack Obama has expressed a willingness to negotiate with Russia and Iran about how to end the Syrian conflict, a five-year war resulting in the loss of more than 250,000 lives. Millions of refugees have fled the country. Russia and Turkey have proposed a meeting that would include the United States, Russia, Saudi Arabia, Iran and Turkey.

The Saudi foreign minister also said that his country hasn't said "no" to sitting down with the Iranians. But he called Iran "an occupying force in Syria" and said it cannot be part of the solution until it withdraws its forces from the country.

Jubeir said the best option would be for Assad to accept the principles of the Geneva I agreement signed at a peace conference in 2012, laying the groundwork for a transitional government.

Under this plan, he said, Assad would immediately cede power to an executive council made up of both members of his regime and opposition figures.