The government recorded 1,630 new coronavirus cases on Monday, sharply lower than Sunday's tally of 2,101, taking the accumulated total since the beginning of the pandemic to 85,005.
The death toll passed the 400 mark, however, rising by 22 to 421.
The Centre for Covid-19 Situation Administration (CCSA) said on Monday the fatalities comprised 13 victims in Bangkok, two in Chiang Mai and one each in Chachoengsao, Khon Kaen, Maha Sarakham, Pathum Thani, Rayong, Samut Prakan and Suphan Buri.
CCSA assistant spokeswoman Apisamai Srirangson said two died the same day they received their test results, while seven others passed away within a week of their diagnoses.
"These cases confirm that if you develop symptoms, you should contact officials for testing as soon as possible," she said.
The number of new cases in Bangkok dropped by almost by half from the 980 recorded on Sunday to 565 on Monday, but the capital still logged more cases than any other province. Nonthaburi came second with 158 cases, followed by Samut Prakan (116) and Samut Sakhon (85).
Clusters under close surveillance in Bangkok were Soi Phetchaburi 5 and 6 in Ratchathewi district and an office building in Yannawa district, she said.
There were also eight imported cases logged on Monday, one case from each of eight different countries — Bahrain, Croatia, India, Ireland, Qatar, Russia, Turkey and the United States.