Police are investigating whether three Friday morning bomb attacks in Bangkok were linked to a similar incident last night at police headquarters.

The explosions hit the Chaeng Wattana Government Complex, a location on Rama IX Road, the Administrative Court, BTS Chong Nonsi and a Ministry of Defense building. A sixth incident in the Pratunam was later determined to be a fire, and it was unclear if it was related.

Ball bearings were scattered in the road at BTS Chong Nonsi, where the Erawan Medical Center said the first bomb hit during morning rush hour.

Update: 2 arrests linked to Bangkok bombing spree: PM

Traffic news site JS100 reported a second detonation that took place at a grassy area on Rama IX Road, near Soi 57/1 in Bangkok’s Suan Luang district. And just before 10am, a bomb reportedly exploded at the Government Complex in Chaeng Wattana.

Police on the scene at BTS Chong Nonsi were unclear where the blasts occurred. One said under the skywalk and another said in a garden in front of the MahaNakorn Tower.

A street sweeper was said to have been injured in Rama IX Road explosion and rushed to Sirindhorn Hospital.

The explosions occurred as US Secretary of State Mike Pompeo was delivering an address in the capital at an annual ASEAN summit.

They come just a day after an EOD team destroyed what was said to be a fake bomb outside the headquarters of the Royal Thai Police.

The last time a bomb attack hit Bangkok was in August 2015 when a terrorist attack destroyed Erawan Shrine during rush hour when it was packed with tourists. Twenty people were killed in an attack blamed on Chinese Uighurs.

Prior to that, a series of bombs ripped through the capital on New Year’s Eve in YEAR. That attack was blamed on separatists in the restive south.

The Deep South, where thousands have been killed in a 15-year insurgency, has been roiling with anger in recent weeks over the death of a suspect in military custody.

This story is developing and will be updated as more information becomes available.

Related story:

Bomb scare shuts down area around BTS Siam during rush hour

Erawan bombing suspect claims innocence, says ‘I’m not an animal’

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