The bodies of an American citizen and a Thai woman were found on Mai Khao beach in Phuket on Monday, police said, while a Russian man drowned off Surin beach on Sunday.
Pol Lt Col Ranaphoum Permpoon, the chief investigator at Tha Chatchai police station, said local residents informed police that two bodies had washed ashore on the beach in Thalang district.
The officer said the deceased man was identified as James Newman, 45, an American citizen, and the woman only as Waranya, 49, a nurse from Surin. The officer also did not reveal the relations between the two.
Investigators found no trace of assaults on them, he added.
A preliminary investigation found they checked into a hotel on Mai Khao on Sunday.
Pol Lt Col Ranaphoum said police believed the two were swimming when one of them was swept away from the beach by the strong current while the other tried in vain to help.
The victims were sent to Vachira Phuket Hospital for an autopsy to pinpoint the cause of the deaths.
Newman was the second US citizen to drown off Phuket in less than two weeks. James Du Bois was found washed ashore last Tuesday at Nai Harn beach in Muang district.
On Sunday, Russian Apostolov Aleksei, 64, drowned off Surin beach in Thalang.
Pol Lt Kittipong Kongkaew, the deputy chief investigator at Thalang police station, said on Sunday police found no signs of violence on Aleksei's body.
The Russian man had stayed at a condominium in Tha Lang. His body was also moved to Vachira Phuket Hospital.
Lifeguards have warned beachgoers to be extremely cautious about rough seas and put up red flags on beaches deemed unsafe for swimmers.