The six had last been seen alive when food was delivered to the room on Monday afternoon. The staff saw one woman who received the food, and security footage showed the rest arriving one by one to the room shortly after.
No-one was seen leaving and the door was locked from the inside. A hotel maid found the bodies on Tuesday afternoon when they failed to check out of the room.
Officers said a seventh person whose name was part of the hotel booking was identified by police as a sibling of one of the six victims, who left the country on July 10. Police believe the seventh person had no involvement in the deaths.
When asked if the news would affect a conference with Russian energy minister Sergei Tsivilev at the hotel later on Wednesday, Mr Srettha said it was unlikely. "This wasn't an act of terrorism or a breach in security, everything is fine."
Mr Trairong said a mass suicide was also unlikely because some of the victims had arranged future things for their trip, such as guides and drivers.
He added that the bodies were not grouped in the same place - some were in the bedroom, some in the living room - suggesting that they did not knowingly consume poison and wait for their death together.
In 2023, the country was rocked by reports of a serial killer who poisoned 15 people with cyanide over a span of years.
Sararat Rangsiwuthaporn, or "Am Cyanide" as she would later be called, killed at least 14 people who she owed money to and became the country's first female serial killer. One person survived.
Police said victims had booked several rooms at the Grand Hyatt Erawan under seven names, and some were staying on a different floor from the room where they were found dead.
Thailand’s Matichon newspaper and other Thai media initially reported a shooting in the country’s capital on Tuesday evening, citing local police.
However Matichon later said the cause of death had been established as poisoning.
Thailand’s prime minister Settha Thavisin has ordered a swift investigation into the incident to stem any damage to the tourism sector.
Thai media reported that the prime minister visited the scene and appeared “stressed” as he refused to give any interviews to journalists at the scene.
A police official, speaking on condition of anonymity, dismissed earlier reports in Thai media that the six people had been killed in a shooting.
"There is no sign of a shooting," the official told Reuters, without elaborating further.
Police officers found the bodies of the six deceased foreign nationals after receiving a call from the hotel's staff at around 5.30pm.
The Grand Hyatt Erawan is described on its website as a five star hotel in the capital’s key commercial and diplomatic district, next to Erawan Shrine. It has 380 rooms and 44 suites and its luxury facilities include a spa and restaurant.
MICHAEL HOWIE|JOSH SALISBURY|MIRIAM BURRELL
