Southern groups are believed responsible for the series of bombings in Bangkok last Friday, Thai authorities said.

Thai Deputy Prime Minister Prawit Wongsuwan said police believed a mastermind was behind the explosions but have yet to establish if they were politically motivated.

“The incidents were planned. We are tracing how they (suspects) travelled and where they got the bombs from,” he told the media after the weekly cabinet meeting at the Government House in Bangkok today.

He said police have not ruled out any motive for the blasts which involved “many” people.

Prawit, who oversees security matters, briefed the cabinet on the explosions, which rocked the capital at a time when it was hosting the Asean Foreign Ministers Meeting.

Last Friday, police found nine bombs, including several unexploded devices, at five locations in the capital city after several small explosions left four people injured.

Meanwhile, Prime Minister Prayuth Chan o-cha said police had arrested seven suspects in connection with the explosions. 

However, he did not disclose when and where they were arrested. He said police were intensifying their hunt for more suspects.

So far nine suspects have been arrested to facilitate investigations. The other two men from Narathiwat were arrested for allegedly planting explosive devices at the sidewalk near the Royal Thai Police headquarters in Rama I Road on Thursday evening.

Prayuth said he would be travelling to Yala in southern Thailand tomorrow to hold discussions with the relevant authorities to find solutions for the decades-long conflict in the region.

- Bernama