BANGKOK — Six people, including two Vietnamese Americans, have been found dead inside a luxury hotel room in central Bangkok, with Thai police exploring the possibility that they were poisoned.

The bodies were discovered by staff in a fifth-floor room at the Grand Hyatt hotel, after the guests missed check-out time by more than 24 hours, according to Thiti Saengsawang, Bangkok’s Metropolitan Police commissioner.

Police said the incident didn’t appear to be a robbery, and none of the bodies showed any signs of suffering physical violence. Police also believe “they didn’t harm themselves.”

But Thiti said cups with traces of a white powder were located in the room, along with untouched food that had been ordered earlier. Poisoning has not been ruled out, Thiti said.

Authorities are currently searching for the seventh person who was part of the hotel booking, and is now a possible suspect.

The other four deceased are Vietnamese nationals. Thiti said police believe one member of the party tried to reach the door but fell before they were able to do so.

Police were pictured guarding the entrance of the five-star hotel on Tuesday, after the bodies were discovered.

The US State Department said it was “aware of reports of the deaths of two US citizens in Bangkok.”

“We offer our sincere condolences to the families on their loss. We are closely monitoring the situation and stand ready to provide consular assistance to those families,” State Department spokesperson Matthew Miller told a briefing Tuesday.

“Whenever a US citizen dies in a foreign country, local authorities are responsible for determining the cause of death. We do reach out to local authorities often to communicate with them when it involves the death of a US citizen and we will certainly be doing so here,” Miller said.

Miller said he did not know if the deaths came up during Secretary of State Antony Blinken’s call with his Thai counterpart, as the call may have taken place before the agency was aware of the deaths.

Last year Sararat Rangsiwuthaporn, a Thai woman who was arrested on suspicion of murdering her friend with cyanide, was charged with at least 13 counts of premeditated murder, in a separate poisoning case that stunned the country. — CNN