An additional 61 service members of South Korea's anti-piracy naval unit in waters off Africa have tested positive for the coronavirus, bringing the total caseload on their destroyer to 68, officials said Sunday.

The figure is feared to rise further, as the test results of about 200 service members of the 300-strong Cheonghae Unit are expected to be available in the coming days.

"Until now, we've received the test results on 101 service members, and 68 tested positive, with 33 negative," an official of South Korea's Joint Chiefs of Staff (JCS) said.

Currently, 15 people, including three infected sailors, are under treatment at local hospitals, and others with mild or no symptoms have been placed in isolation on their vessel, the Munmu the Great, the official said.

The government decided to bring back all the unit members home and sent two KC-330 Cygnus multirole aerial tankers to Africa on Sunday, kicking off an operation codenamed "Mission Oasis."

The aircraft left Gimhae International Airport in the southern city of Busan at 4 p.m., carrying around 200 Korean personnel, including 13 medical members, as well as 148 troops tasked with sailing the destroyer back home, according to the ministry.

"We've implemented thorough antivirus measures and loaded enough, necessary medical and other supplies to ensure their safe return at the shortest possible time," a ministry official said. "Upon arrival, they will undergo virus tests again and be sent to facilities for quarantine and treatment."

The aircraft are expected to arrive back home Tuesday, if the related process goes smoothly, he added.

Their return will be about a month ahead of original schedule, which will mark the first early return of the contingent since the unit was first deployed in 2009. The troops are rotated every six months for an anti-piracy mission in the Gulf of Aden off Somalia's coast and around the Strait of Hormuz.

A replacement contingent is on its way after departing for Africa last month to take over the mission.

"Three of the patients require intensive care, but the medical staff judges that they still are able to be airlifted by the aerial tankers," the official said.

"We are also preparing for different options, including sending another aircraft equipped with advanced medical equipment. We are closely monitoring the situation," he added.

Contact tracing is under way, but the infections appeared to have begun after the vessel was docked at a nearby port for days late last month to load supplies.

The military has come under criticism for its poor initial response to the outbreak and the lack of guidelines on such a pandemic.

The sailor who first developed symptoms was found to have been given only cold medicine. A dozen others who later showed similar symptoms were tested for the virus with rapid testing kits, instead of more accurate PCR tests.

Some also claimed the authorities did not actively seek ways to inoculate the unit members, overlooking the possibility of infections as they all tested negative in tests conducted before their departure in February and they are supposed to stay on the vessel without much contact with others.

None of the troops have been vaccinated, as they left South Korea just before the country began its inoculation campaign.

"There could be difficulties in responding to possible emergency cases if troops had serious cases of side effects were they to get vaccinated on the vessel, and the destroyer does not have facilities required to store vaccines," a ministry official said, explaining reasons for not administering vaccines to the service members.

"We are talking and will continue to take measures to ensure their safe return home and treatment," a ministry official said.

Up until now, around 73 percent of some 1,300 troops on overseas missions have been fully vaccinated, including all members of the new batch of the Cheonghae unit, according to the ministry. (Yonhap)