2 U.S. citizens among 6 dead in suspected poisoning in luxury Bangkok hotel

July 16 (UPI) -- Six people were found dead in an upscale hotel in Thailand's capital city in a possible murder by poisoning that claimed two Vietnamese-American as victims, officials say.

Three men and three women, who were four Vietnamese nationals and two Vietnamese-Americans, were found dead on the fifth floor of the five-star Grand Hyatt hotel near the Erawan Shrine -- the site of the deadly 2015 bombing that killed 20 people -- in downtown Bangkok after failing to check-out.

While poisoning is not yet listed as the official cause of death, it has not been ruled out, according to Thiti Saengsawang, Bangkok's Metropolitan Police commissioner.

Police are looking for a seventh person who is said to be part of the hotel booking and who is unaccounted for. The case is being treated as a likely murder and not a suicide, law enforcement officials said.

"From the preliminary examination of the scene, it was assumed that they had been poisoned," Police Maj. Gen. Theeradej Thumsuthee, chief investigator of the Metropolitan Police Bureau, said on Thai television.

Four of the bodies were located in the living room and two in a bedroom. The room was found to be locked from the inside after the bodies were discovered, along with their packed bags. That discover was made by a maid after the victims did not check out as scheduled on Tuesday.

Authorities say it does not appear to be a robbery and none of the bodies showed signs of physical violence, leading police to say the victims "didn't harm themselves."

However, cups of coffee and tea with traces of white powder were found in the room and untouched food previously brought by room service. The food was supposedly brought around 1 p.m. local time on Monday and the hotel employee who delivered it will reportedly be interrogated.

All of the victims arrived at Bangkok's Grand Hyatt Erwan Hotel on July 13 and the next day and were staying in five different rooms, officials say, and it is believed there are family relations as many of them have the same last name.

"We are tracing every step since they got off the plane," Sangsawang told reporters Tuesday local time in Bangkok.

The country's prime minister visiting the scene told reporters the victims had been found at approximately 4:30 p.m. local time on Tuesday and confirmed the crew had been dead for about 24 hours by that point.

"From initial dead body inspection, the cause of dead could be from something they consumed," Thai Prime Minister Srettha Thavisin said Tuesday in Bangkok.

The State Department said Tuesday it was "aware of reports of the deaths of two US citizens in Bangkok," offering condolences to the families and saying how the United States is "closely monitoring the situation" and will be ready to "provide consular assistance to those families."

"Whenever a U.S. citizen dies in a foreign country, local authorities are responsible for determining the cause of death," State Department spokesperson Matthew Miller said. "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."