A forensic examination at Police General Hospital in Bangkok had confirmed that Ukraine ambassador Andrii Beshta died of a heart attack, the Royal Thai Police Office said on Monday afternoon.
The statement said there were no traces of physical assault on the body, and no evidence of forced entry into the resort room where he was staying at the time on Koh Lipe, in Satun.
The cause of death was heart failure.
Nathapong Latthapipat, deputy director-general of the Foreign Ministry's Department of Protocol, arrived at the hospital at 11am to receive the body, the statement said.
The body would be moved to Wat Thep Sirinthrawat Ratchaworawihan, in Bangkok's Pom Prap Sattru Phai district. for funeral rites from June 1-4. A royally-sponsored cremation would be held on June 5.
Beshta died on Sunday morning, aged 45 years, while on a vacation with his son and friends on Koh Lipe.
Government spokesman Anucha Burapachaisri said on Monday that Prime Minister Prayut Chan-o-cha was deeply saddened by the ambassador's death.
Beshta had been the Ukraine's ambassador to Thailand since 2015. He was due to end his term in the third week of June. As ambassador he had played an important role in forging ties and cooperation between Thailand and Ukraine.
Governent agencies would provide the family with all convenience and due honour, Mr Anucha said.