Thai police have arrested three teenagers as suspects following a series of bomb blasts that rocked Bangkok.

The arrests matched a description police gave to The Straits Times that local residents saw several technical school students dropping off objects before some of the explosions took place on Friday.

The six explosions were believed to be caused by home-made bombs triggered by timers, investigators have said.

One of the blasts took place on Rama 9 Road in Suan Luang district and injured three street cleaners.

A seventh unexploded device was later recovered by the authorities.The security scare added to the two fake bombs found by police on Thursday near the Centara Grand and Bangkok Convention Centre, where the 52nd Asean Foreign Ministers’ Meeting and related gatherings were being held.

Two men have been arrested in connection with the fake bomb incident.

Meanwhile, a fire, suspected to be an arson, broke out in the commercial district Siam Square on Friday. A manhunt has been launched for a man acting suspiciously according to a store’s surveillance footage.

Footage showed an explosion at the mall – which is minutes from the summit venue – in the early hours of Friday morning, after it was apparently planted by a man dressed in a student’s uniform about 12 hours earlier.

The man, wearing a fedora and face mask, is seen entering a store in the mall at around 3:30pm on Thursday, according to time stamps on the footage.

Milling around the store, he stops at a shelf full of cuddly toy seals and polar bears and fiddles with one of them for a few seconds before placing it back on the shelf.

Prime Minister Prayut Chan-o-cha has ordered a probe into the bomb attacks and the other incidents.

No group has claimed responsibility for the blasts, and it was not immediately known if all of the attacks were linked.

Prayut said at a news conference on Friday that an “old group” could be the possible culprits behind the explosions, which could be personally embarrassing to him as he played host for the high-profile meeting after being controversially elected prime minister in June by parliament, following the March general election.

He was referring to his political rivals the Red Shirt group, comprising supporters of former prime ministers Thaksin and Yingluck Shinawatra.

“But I am not ruling out other possibilities,” Prayut added. THE STAR (MALAYSIA)/ASIA NEWS NETWORK