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.
Police said local residents told police that two bodies had washed ashore on the beach in Thalang district.
The dead man was identified as James Newman, 45, an American, and the woman only as Waranya, 49, a nurse from Surin.
Police found no trace of assaults on them.
An investigation found they checked into a hotel on Mai Khao on Sunday.
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.
They were sent to a hospital for an autopsy.
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.
On Sunday, Russian Apostolov Aleksei, 64, drowned off Surin beach in Thalang.
Police found no signs of violence on Aleksei's body.
The Russian man had stayed at a condominium in Tha Lang.
Lifeguards have warned beachgoers to be extremely cautious about rough seas and put up red flags on beaches that are unsafe for swimmers.
