The United Nations has called for Myanmar to hold to account anyone using excessive force against unarmed civilians after security forces rammed a car into an anti-coup protesters killing five of them, according to media and witnesses.

Photographs and videos posted on social media showed a speeding vehicle crashing through a group of anti-coup protesters on Sunday in the main city of Yangon and bodies lying on the road. Witnesses said dozens had been injured.

"Those responsible for the use of excessive and disproportionate use of force against unarmed civilians must be held to account," Ramanathan Balakrishnan, the U.N resident coordinator in Myanmar, said in a statement.