ULAN BATOR -- More than 20 Mongolian people tested positive again for COVID-19 after they had recovered and been discharged from hospital, the country's National Center for Communicable Diseases (NCCD) said Tuesday.

"At least 23 out of 213 COVID-19 patients who had recovered and been discharged from the NCCD have tested positive again for the virus," Amarjargal Ambaselmaa, head of the NCCD's surveillance department, said at a daily press conference.

"However, our citizens have nothing to fear," said Ambaselmaa, because the 23 people retested positive when they were in 14 days of further observation at special facilities.

Meanwhile, Mongolia conducted 520 tests for COVID-19 in the last 24 hours and the results were all negative, with the national tally remaining at 287, the NCCD said in a statement.

All the 287 confirmed cases are imported ones, mostly from Russia, according to the center.

The country has reported no local transmissions or deaths so far.