This file photo, taken Feb. 13, shows Asiana Airline and Koren Air aircrafts at the Incheon International Airport in Incheon, west of Seoul. Yonhap

The combined value of unused miles with Korea's top two airlines reached 3.5 trillion won ($2.58 billion) as of June, data showed Sunday, amid the extension of expiration dates following travel disruptions caused by the COVID-19 pandemic.

The amount of such deferred income for Korean Air Lines and Asiana Airlines stood at 2.52 trillion won and 975.8 billion won, respectively, as of the end of June, according to their regulatory filings.

Compared with a year earlier, the value of unredeemed miles for Korean Air and Asiana Airlines increased 4.5 percent and 3.5 percent, respectively.

While the operators implemented a policy in 2008 to set a 10-year expiration period for miles, they announced plans to extend the expiration date by up to three years during the pandemic.

Experts say the airlines have been making efforts to encourage customers to use their unredeemed miles to avoid potential hurdles in the process of Korean Air's acquisition of Asiana.

Korean Air is in the process of acquiring Asiana and has so far obtained approval from 13 countries and regions for the acquisition, with the final nod yet to come from the United States to complete the merger plan. (Yonhap)