A security guard at a nightclub on Khao San Road has been charged with assault after a video clip of him slapping and handcuffing a foreigner surfaced on social media.

The management of The Club Khaosan, where the incident occurred, has issued an apology.

A police complaint was filed against the security guard, who was then sacked.

Police said the guard -- identified as Thongchai -- has been detained and charged with assault.

According to police, the incident occurred at about 2am on Saturday when Mr Thongchai was told by club staff that a foreign man -- whose name and nationality were not known -- had stolen a bottle of water.

When confronted by Mr Thongchai, the man admitted he took it from inside the club, believing it was free, police said.

Mr Thongchai said an argument with the foreigner ensued. Following some miscommunication, he became angry and put the foreigner in handcuffs and slapped him twice in the face. Another guard intervened and told the suspect to stop, police said.

A local who was walking past the club took a clip of the incident, which was later posted on social media before going viral, police said.

Mr Thongchai was later taken to Chana Songkhram police station for investigation before he was charged with assault. Police were looking for the foreign man to get more information from him.