Six people found dead in a Bangkok hotel room are said to have been "poisoned with cyanide by an American woman", authorities in Thailand believe.

Traces of cyanide were found in the cups of six Vietnamese and American guests at a central Bangkok luxury hotel, with initial investigations finding that one of them is believed to have poisoned the others over a bad investment, the Thai Police say. "We are convinced that one of the six people found dead committed this crime," Bangkok deputy police chief Noppasin Punsawat said.

Police Lieutenant General Thiti Saengsang added: "This was not self-harm - someone caused the deaths. We are tracing every step since they got off the plane." The bodies were found Tuesday in the Grand Hyatt Erawan Bangkok, a landmark at a central intersection in the capital busy with malls, government buildings and public transit.

Sherine Chong, 56, is thought to have poisoned herself and five others
The poisoned cups (
Image:
ROYAL THAI POLICE/HANDOUT/EPA-EFE/REX/Shutterstock)

The six had last been seen alive when food was delivered to the room Monday afternoon. The staff saw one woman receive the food, and security footage showed the rest arriving one by one shortly after. There were no other visitors, no one was seen leaving and the door was locked. A maid found them Tuesday afternoon when they failed to check out of the room.

Forensic police chief Trairong Piwpan said a mass suicide was unlikely because some of the victims had arranged trips and booked guides and drivers. He added that the bodies were not grouped in the same place, with some in the bedroom and some in the living room. He said they did not knowingly consume poison and wait for their death together.

They had dinner at the hotel (
Image:
ROYAL THAI POLICE/HANDOUT/EPA-EFE/REX/Shutterstock)

On Wednesday, Noppasin disclosed that a seventh individual, whose name was part of the hotel booking, was a sibling of one of the six and had left Thailand on July 10. Police suspect this person had no involvement in the deaths. Prime Minister Srettha Thavisin confirmed that the Vietnamese and United States embassies have been informed about the deaths, and the American FBI was en route.

The case is not expected to impact a scheduled conference with Russian Energy Minister Sergei Tsivilev at the hotel later on Wednesday, according to officials. "This wasn't an act of terrorism or a breach in security. Everything is fine," reassured one official.

Police block media from entering the Grand Hyatt Erawan (
Image:
Getty Images)

The possibility of a mass suicide was ruled out by Thai police force's forensic division commander, Trairong Piwpan, as some of the victims had made future travel arrangements such as hiring guides and drivers. The scattered locations of the bodies within the hotel room suggest they did not knowingly ingest poison and wait for their deaths together.

Matthew Miller, a spokesman for the US State Department in Washington, expressed condolences to the families of the victims. He confirmed that the US is closely monitoring the situation and will maintain communication with local authorities. US Secretary of State Antony Blinken had a conversation with his Thai counterpart on Tuesday. However, Miller believes this call took place before the deaths were reported and he is unsure if the incident was discussed.