US President Donald Trump called out Russian President Vladimir Putin by name on Sunday for backing Syrian President Bashar al-Assad and warned of a "big price" after reports of a chemical weapons attack in Syria almost a year to the day since the US struck a Syrian air field after a previous attack, CNN reported.

"Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price to pay. Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK!" Trump tweeted.