A British dual national was arrested for allegedly murdering a Japanese tourist in Thailand.

The Brit, David Maensiri, 36, was said to be having a row with his girlfriend when Japanese passer-by Seita Tanabe, 27, tried to intervene.

However, David allegedly turned his fury on the well-meaning holidaymaker, sparking a punch-up in Thai 'Sin City' Pattaya on December 29.

The suspect, who also has Thai nationality, was said to have pulled out a knife during the altercation which he plunged deep into Seita's chest.

Footage shows David being handcuffed and hauled into a pickup truck.

Police Captain Wuttikorn Plodprong of the Pattaya City Police Station said cops received a report at 6:06 am.

They arrived at the scene, where medics were performing CPR on Seita who had a deep wound on his chest. He was rushed to a hospital but later succumbed to his injuries.

Officers detained a bruised David and hauled him onto a police truck. He was described as drunk and remorseless, even flashing a cheeky rock-and-roll hand sign at the cops. He was taken to a hospital for a dislocated shoulder, abrasions, and head injuries.

Police Captain Wuttikorn Plodprong of the Pattaya City Police Station said: 'We have inspected the scene and taken photos as evidence. We are collecting more evidence in order to take legal action against the suspect.'

A witness named Bank, 22, said he and Seita had noticed the suspect arguing with his girlfriend.

He said: 'We tried to intervene, but the boyfriend misunderstood and ended up punching the Japanese man in the face. They separated, but not long after, the Japanese tried to retaliate with another punch, causing another scuffle.

'Everyone tried to stop them but it was too late. The suspect pulled out a knife and stabbed the Japanese in front of everyone.'

Dashcam footage shows Seita in a white shirt charging at the Brit from across the street. Seita's girlfriend was heard calling out to stop him.

Deputy Inspector Itthiporn Tangchuthaweesap of the Pattaya City Police Station said: 'A meticulous investigation is ongoing to build a case against the suspect. The aim is to ensure legal proceedings are pursued thoroughly and justly.'

Former fishing village Pattaya became popular with American troops on 'rest and relaxation' breaks in the 1960s when the U.S. military had bases in Thailand. In the ensuing years, the coastal resort spawned into a semi-barbarous sex-tourism destination.

Embarrassed officials have made progress in gentrifying the region with family tourism projects but a ravenous nightlife industry and corrupt police have hampered their efforts, with undesirables from all nations still attracted to the seedy city.