South Korea's daily new coronavirus cases fell back to the 1,300s on Tuesday due to fewer tests over the extended weekend amid concerns over a potential upsurge down the road.

The country added 1,373 more COVID-19 cases, including 1,323 local infections, raising the total caseload to 226,854, according to the Korea Disease Control and Prevention Agency (KDCA).

Daily infections fell from 1,556 on Monday, 1,817 on Sunday and 1,930 on Saturday, but the decline was attributable to fewer tests over the three-day holiday.

The country added six more deaths from COVID-19, raising the death toll to 2,173. The fatality rate was 0.96 percent.

Since early July, South Korea has been grappling with the fourth wave of the pandemic amid the fast spread of the more transmissible delta variant and slow vaccinations.

For more than a month, the greater Seoul area, home to half of the country's 52 million people, has been under the toughest virus curbs, and some regions outside the greater Seoul area are also under the toughest virus restrictions.

Despite the Level 4 distancing rules, the number of daily infections has topped 1,000 for 42 days in a row. The country reported a record high 2,223 cases Wednesday.

Health authorities said they are reviewing more enhanced antivirus measures to contain the pandemic.

A delay in the vaccine supply by US drugmaker Moderna Inc. is also complicating the country's efforts to accelerate the vaccine rollout.

Moderna has notified the government that it will supply less than half of the 8.5 million doses of its COVID-19 vaccine planned for August.

The supply setbacks have raised doubts over the government's plan to administer the first shots to 70 percent of the population, or 36 million people, by Sept. 19 and have them fully vaccinated by the end of October to achieve herd immunity.

On Monday, President Moon Jae-in said that health authorities will have administered second shots to 70 percent of the country's population by the end of October.

As of Tuesday, 23.05 million people, or 44.9 percent of the population, had received their first shots of COVID-19 vaccines, the KDCA said.

The number of fully vaccinated people stood at 9.99 million, or 19.5 percent.

Of the locally transmitted cases, Seoul reported 361 new cases, and Gyeonggi Province, which surrounds the capital city, identified 372 new patients. The southeastern port city of Busan reported 65 more cases, and Incheon, 40 km west of Seoul, added 77 cases.

The number of new imported cases came to 50, raising the total to 12,919.

The number of patients with serious symptoms across the country reached 354, up one from a day earlier, the KDCA said.

The total number of people released from quarantine after making full recoveries was 197,224, up 1,026 from a day earlier.