At least six Vietnamese nationals were found dead in a luxury hotel suite in the Thai capital Bangkok, Thai police said.
According to the government, some of the dead were Vietnamese-Americans.
Local media initially reported that the shooting occurred at the five-star Grand Hyatt Erawan Bangkok hotel, but police dismissed these reports and said there was no evidence of a shooting.
Local media reported that police believe the victims may have been poisoned, but this has not been confirmed and the cause of death remains unexplained.
Thai Prime Minister Sreta Thavisin, who visited the scene, ordered an investigation into the deaths and said he hoped the incident would not harm the country's image or impact tourism.
He said police estimated the victims had been dead for more than 24 hours and that autopsies would be performed to determine if they had eaten anything.
Police suspect there may be a seventh Vietnamese national, but that person has not yet been found, he added.
Earlier, Thai public broadcaster quoted police as saying three women and three men were killed.
Police Major General Tiradechi Tamsute told the broadcaster that initial investigations suggest the victims were poisoned.
“There were no signs of a struggle,” PBS reported. “Tea and coffee cups were found to have been used.”
Police were dispatched to the hotel around 5:30 p.m. local time after receiving a call from hotel staff.
