During an investment forum in Riyadh, Oliver Stone praised Russian President Vladimir Putin as a "stabilizing force" in the Middle East, particularly in Syria, which has been plagued by bloody war for years.

Stone, a leading critic of US foreign policy for decades, has long regarded Putin as a "man of peace" and has produced a controversial documentary work in 2017, including a series of interviews with the Russian president.

"Putin is a stabilizing force in the Middle East, specifically in Syria, in contrast to the United States," Stone said on the second day of the Future Investment Initiative Forum.

Russia supported the regime of Syrian President Bashar al-Assad in a conflict that has killed hundreds of thousands.

Last week, Russia and Turkey signed an agreement under which Russian military police and Syrian border guards would facilitate the withdrawal of Kurdish forces 30 kilometers from the Turkish border, in an attempt to reduce the escalation after a Turkish operation in northern Syria. Stone said the Russian president "was worried about the terrorists. If they had arrived in Damascus, there would have been a caliphate in the whole region."