All the dead were of Vietnamese origin, two of them American citizens and four Vietnamese citizens, Sreetha said, adding that he had spoken with the Vietnamese ambassador.

The prime minister said the victims were believed to have been dead since Monday. He added that there were no immediate signs of robbery or assault, and that the initial investigation focused on the possibility that the visitors had ingested a harmful substance.

The initial conclusion among investigators is that the person responsible for the deaths was not among the dead, said Lt. Gen. Thiti Sangsawang, commissioner of the Bangkok Metropolitan Police Office.

“We are not saying they were poisoned, but we are looking at the possibility that their lives were deliberately targeted, and there are suspicions that someone intended to harm or kill this group of people,” he said at the press conference.

The deaths of six foreigners at a luxury hotel in the Thai capital could come as a shock to a country whose economy relies heavily on the tourism industry.

“Hyatt is deeply saddened by this tragic situation,” Angelina Hu, a spokeswoman for Hyatt’s Asia Pacific region, said in an emailed statement. “The safety and security of our guests and colleagues is always our top priority.” Hyatt is cooperating with local authorities and has referred further questions to the police, she added.

Vietnam’s Foreign Ministry said in a statement to The Washington Post that Vietnamese Ambassador to Thailand Pham Viet Hung went with embassy officials to the hotel and that the embassy is working closely with local officials “to monitor the incident, clarify information, identify victims and implement necessary citizen protection measures.”

A US State Department spokesman said in a statement that the department is “aware of the reports.” [of] “Two US citizens killed in Bangkok.”

“The State Department is closely monitoring the situation” and “stands ready to provide consular assistance,” the State Department spokesman said.

“When a U.S. citizen dies in a foreign country, local authorities are responsible for determining the cause of death,” the State Department spokesman said, referring to Thai authorities. “Out of respect for the families of the victims during this difficult time, we have no further comment.”

Representatives from the Thai Foreign Ministry and the U.S. embassies in Bangkok and Hanoi did not immediately respond to requests for comment Tuesday evening local time.

the pictures Photos of the room where the bodies were found showed an array of room service food and cups of tea. Most of the food appeared to be untouched, with plastic wrap still covering some of the dishes.

Police Commissioner Thiti said that although no food had been consumed, the drinks appeared to have been “completely consumed” from the glasses, with residue at the bottom. He added that the residue had been collected as evidence.

He added that the dead were not injured, except for one person who suffered a “facial injury” that appeared to have been caused by falling on a hard surface, rather than a blow.

The room was locked from the inside, Thiti said. When the occupants did not leave the room as planned, a maid entered through the back door and found the bodies, he added. Management then called the police.

Thiti said four bodies were found in a living room and two in a bedroom. The people had checked into the hotel at different times and occupied five rooms on two floors of the hotel.

The commissioner said the individuals had their luggage moved into one of their rooms, “suggesting that these individuals knew each other.” The hotel told police that payment for the stay had not been settled.

He added that authorities were looking at table settings, items left in the room, guests’ luggage, CCTV footage and visitors’ social media profiles to try to figure out what happened.

This report was prepared by Welawan from Bangkok, with Rebecca Tan from Singapore contributing to this report.