BANGKOK (AFP) - Thailand's military has detained a man for questioning after the car bomb attack which wounded seven people on the resort island of Samui as security was tightened there, police said Sunday.

Military officers detained the man for questioning late Saturday in Nonthaburi province, on the northern outskirts of Bangkok, in connection to the explosion, national police spokesman Prawut Thavornsiri told AFP.

"Authorities have brought in a man for questioning after finding a threatening post on his Facebook page," Prawut said, adding the post had appeared Friday before the blast.

"As far as I know, he is still in military detention for further investigation," he said.

Security in the tourist hub has been tightened since the car bomb in a mall car park went off Friday, injuring six Thais and a 12-year-old Italian girl.

Extra police officers have since been deployed as Thailand enters the busy Songkran new year holiday period, Prawut said.

"We have sent more police to check the airport and ferry port," he added.

The blast comes a week after Thailand's junta, which seized power last May, replaced martial law with sweeping security powers retaining the military's control including the right to arrest and detain people for crimes such as breaching national security.

It has justified the new measures, widely criticised by the international community, as essential to curb the threat of political unrest, recently blaming anti-coup groups for a series of small bomb attacks in Bangkok earlier this year.

On Saturday Prawut said the car used in the Samui bomb attack had been stolen from Yala, one of Thailand's three southernmost Muslim-majority provinces that have been scorched by a 10-year insurgency that has killed more than 6,300 people.

But he did not specify whether the blast was believed to be linked to that conflict - which is hundreds of kilometres away and which has so far remained highly localised.

Thai police have previously been accused of leaping to conclusions in the immediate aftermath of high-profile incidents.

They came under fire during the probe into the murder of two British backpackers on Koh Tao island last year for bungling the initial investigation.

Small bomb attacks and shootings are fairly frequent across Thailand, where the rule of law is weak, and are often attributed to disputes over business, local politics or criminal activities.