A cargo train derailed after an improvised bomb allegedly planted by suspected terrorists exploded along a railway linking Thailand to Malaysia on Saturday.

The train was delivering rubber sheets to Malaysia when the homemade explosive device went off in the Sadao district of Thailand's Songkhla province on December 3 afternoon.

Eleven of its 20 cars were dislodged from the tracks, with the blast leaving a two-metre-deep crater on the ground, State Railway of Thailand officials said.

Four train staff were onboard during the explosion. None of them were injured.

The affected route connecting border towns Hat Yai and Padang Besar has been temporarily closed while repairs and clearing operations are ongoing.

Major General Wara Vechapinan, Songkhla Provincial Police chief, said: 'We believe insurgents are behind the explosion. They are trying to damage the local economy and tourism in the area.'

He added that government officials were planning to use the route for tourists travelling between Hat Yai and Kuala Lumpur.

Islamic separatist terror attacks happen regular in the three southernmost provinces of Thailand next to the border with hardline neighbors Malaysia. However, they rarely target civilians and are geared towards hitting Thai state employees and infrastructure.

The three provinces of Thailand - Yala, Pattani and Narathiwat - have been blighted by terrorism for several decades, dating back to a deal in 1909 between the British Empire to incorporate the Muslim region into the main country of Siam.

However, the area's culture is more similar to Malaysia and dramatically different to Buddhist Thais. Following years of tension, armed separatist groups emerged fighting for independence in the 1960s.

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.