At least six people, including two Vietnamese Americans, were found dead inside a hotel room in Bangkok city of Thailand, media reports said.

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, reported CNN.

Police believe the incident was not connected to robbery and their bodies did not show any signs of violence.

Thailand police are exploring a possibility that they were poisoned.

Thiti told CNN that cups with traces of a white powder were located in the room, along with untouched food that had been ordered earlier.

Police are currently searching for another person who was part of the hotel booking and remains a prime suspect.

The US State Department said it is aware of the death of two American nationals in Bangkok.

"We are aware of the reports of the deaths of two U.S. citizens in Bangkok, Thailand. 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," US State Department spokesperson Matthew Miller told a briefing Tuesday.

"Whenever a U.S. citizen dies in a foreign country, local authorities are responsible for determining the cause of death," he said.

"We do reach out to local authorities often to communicate them about – to communicate with them when it involves the death of a U.S. citizen, and we will certainly be doing so here. But I would defer to the local authorities for any further comment on what I believe is an ongoing investigation," he said.