Army chiefs have ordered reinforcements along the Thai border with Malaysia following suspected insurgent attacks in the conflict-plagued south of the country.

Military leaders on Monday doubled the number of patrol units stationed along the river border to intercept illegal crossings in Narathiwat province.

Fourth Army Region commander Lieutenant General Narathip Phoyanok said illegal piers along the Golok River bordering Malaysia were allegedly used by separatist militants to enter and flee Thailand.

He said the army would discuss pier regulations with the Interior Ministry and residents, adding: 'They are part of their way of living along the border.'

Narathiwat governor Boonchuay Homyamyen also convened riverside residents and provincial and district authorities to create guidelines to address the issue.

Officials said people regularly cross the river to visit friends and relatives in Kelantan, Malaysia, avoiding queues at official checkpoints.

Malaysia has reportedly begun demolishing illegal piers on its side, as they were allegedly used for illegal trafficking.

The National Security Council had previously reported more than 900 boats involved in illegal crossings.

The tightened restrictions followed coordinated attacks that struck 11 petrol stations across the southern provinces of Narathiwat, Pattani, and Yala, on January 11.

Thai Prime Minister Anutin Charnvirakul, citing security agencies, said attacks were carried out to disrupt the local elections.

He added that the Fourth Army Region and the Provincial Police Region 9 have been tasked to investigate the explosions.

Martial law and a curfew were also imposed but lifted just a day later as army chiefs said the threat was 'manageable'.

Islamic separatist terror attacks target the three southernmost provinces of Thailand - Yala, Pattani and Narathiwat - next to the border with Mulsim neighbors Malaysia. Thai state employees and infrastructure are often hit while attacks on civilians are rare.

Officials believe the conflict dates to a deal in 1909 that the British Empire struck to incorporate the Muslim region into the Siamese mainland.

The region's culture is more similar to Malaysia and dramatically different to Buddhist Thais causing decades of tension that lead to the emergence of separatist groups fighting for independence in the 1960s.

The struggle has continued ever since with more than 7,344 people killed and 13,641 injured between January 2004 and March 2022.

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.