The second blast at a canal near Saphan Taksin pier last Tuesday intensified anxiety in a city already reeling from the bomb attack at Erawan shrine in downtown Bangkok which killed 20 people and wounded scores more.
"Today the Southern Bangkok Criminal Court approved an arrest warrant against a man of unknown nationality" over the second blast based on CCTV footage, national police spokesman Prawut Thavornsiri said in a statement released late Thursday.
The man has been charged with "illegal possession of an explosive device, illegally detonating a bomb and premeditated attempted murder", he said.
Thai police had been investigating security camera footage showing a man in a blue-shirt kicking a package off a footbridge and into a canal in the same spot where a device exploded last Tuesday, sending people scurrying for cover but causing no injuries.
Speaking to AFP on the telephone, Prawut confirmed the arrest warrant was for the same man seen in that footage.
"We have not yet concluded whether the two blasts are linked to each other," he said when asked whether the second blast was related to the fatal attack at the Erawan.
Ten days on from the shrine blast, which killed 14 foreigners in Thailand's worst single mass-casualty attack, the police have made no arrests.
The majority of those killed were ethnic Chinese worshippers from across Asia, who flocked to the Hindu shrine in the belief that prayers there bring good fortune.
Police have focussed their search for the perpetrator of Monday's attack on a primary suspect in a yellow t-shirt seen placing a heavy rucksack under a bench at the shrine in CCTV footage.
Moments later the blast struck, scattering body parts, glass and debris over a bustling Bangkok shopping district.
An arrest warrant has already been issued for the primary suspect, who is described as an unnamed foreign man with shaggy hair and thick rimmed glasses.
On Saturday Prawut said he believed it was "likely" that two different men carried out the shrine and canal blasts.
The unverified footage of the canal blast which has been widely circulated by local media is time-stamped just a few minutes after last Monday's bombing, which struck at 18:55 pm (1155 GMT).
It shows the man in the blue t-shirt carrying something heavy in a plastic bag. He goes to the side of a footbridge, places the bag down and then uses his mobile phone.
Around a minute later he pushes the bag into the canal with his foot, kicking up a visible splash of water.
The following day, shortly after 1:00 pm on Tuesday, an explosion went off in the canal.
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