All three patients in quarantine facilities were Thais returning from Saudi Arabia, the UK and Sweden.
Meanwhile, two Malaysians who had allegedly crossed into Thailand via a natural channel tested positive outside quarantine.
Among provinces with Covid-19 cases from December 18, 2020, the CCSA said that seven provinces had found new cases in the past 1-2 days, and four provinces in the past 3-6 days.
Six provinces did not report any new case in the past 7 to 14 days, five provinces in the past 15 to 28 days, and 41 provinces in the past over 28 days.
Meanwhile, 58 patients have recovered and been discharged.
As of Sunday, the number of confirmed cases in Thailand had risen to 26,370. Of these, 25,744 had been contracted locally, including 14,681 who were found via proactive testing, while 2,838 were returnees. So far, 25,744 have recovered and been discharged, 541 patients are still in hospitals and 85 have died.
According to Worldometer, as of 10am on Sunday, the number of confirmed cases globally had risen to 117.07 million (up by 405,509), 92.65 million have recovered, 21.82 million are active cases (89,309 in severe condition) and 2.59 million have died (up by 128).
Thailand ranks 115th on the global list of most cases, which is topped by the US with 29.65 million, followed by India 11.21 million, Brazil 10.93 million, Russia 4.31 million and the United Kingdom 4.21.