Two policemen were killed and two others injured when a roadside bomb from suspected Muslim separatists exploded today in Thailand's terrorism-ravaged deep south.

The officers were travelling in a pick-up truck when the device was detonated in the Bannang Sata district of Yala province close to the border with Malaysia at around 10am local time. Pictures of the aftermath show how the truck was flipped over by the force of the blast and into a ditch.

Two officers Lieutenant Colonel Wiwat Rakchat and Lieutenant Natchaphon Phrommanee died at the scene while two others - Lieutenant Colonel Sufrey Norapha and Lieutenant-General Asrawut Rapom - were critically injured and taken to hospital to be treated. They were delivering a court summons for a traffic case when the explosion happened.

Police investigating the blast said a bomb made from a cooking gas tank was planted on the roadside near a bridge over a canal before a detonation cable was trailed into nearby woodland. They believe the killer watched the police car approaching before detonating the device.

Officers said that they believe the police car had been tracked for several miles because the officers 'were not taking a regular route'.

A spokesman said: 'The assailants detonated the bomb when the car arrived, hoping to kill all the officers inside. After the explosion, the suspect relied on his knowledge of the local area to escape.'

The southernmost provinces of Thailand - Yala, Pattani and Narathiwat - were incorporated into the country following a deal between then-Siam and the British Empire in 1909.

However, the region is made up primarily of Malay Muslims with a culture dramatically different to Buddhist Thais and in the 1960s armed separatist groups emerged fighting for independence.

The struggle has continued ever since with more than 7,290 people killed between January 2004 and October 2021. There were an average of 38.8 incidents and 36.7 casualties a month in 2021, according to data from Deep South Watch.

The British Foreign & Commonwealth Office warns against all but essential travel to the region while Canada's government warns its nationals to 'avoid all travel' to the three provinces.