Six Vietnamese nationals who died in a luxury hotel suite in Thailand were likely poisoned by tea laced with cyanide, police have said.

The deceased were found dead by housekeepers at the Grand Hyatt Erawan hotel in the Thai capital Bangkok late on Tuesday.

Investigators believe they had been dead for 24 hours by then.

Authorities are investigating debt as a motive behind the mysterious deaths, saying that two of the six had loaned “tens of millions Thai baht” to another of the deceased for investment purposes.

Confusion and mystery had earlier surrounded the grim discovery of the bodies – with local reports initially suggesting there had been a shooting. Police later dismissed these reports.

A clearer picture is emerging now of what might have happened – with police saying the group of six people had all gathered in a room early in the afternoon on Monday.

In a press conference on Wednesday, Deputy Bangkok police chief Gen Noppassin Poonsawat said the group had checked into the hotel separately and were assigned five rooms – four on the seventh floor, and one on the fifth. The group had all made their way to the room on the fifth floor.

Two of the victims, Sherine Chong, 56, and Dang Hung Van, 55, had dual American citizenship.

The other four were Nguyen Thi Phuong, 46, her husband Pham Hong Thanh, 49, Nguyen Thi Phuong Lan, 47, and Tran Dinh Phu, 37.

The group ordered food and tea, which was delivered to the room around 14:00 local time and received by Ms Chong.

According to the deputy police chief, a waiter offered to make tea for the guests but Ms Chong refused this.

The waiter later left the room – no one else is believed to have entered the room apart from the six inside. Police say there were no signs of a struggle or a robbery.

Police later found traces of cyanide in all six tea cups.