Two Chinese fighter jets skirted the fringes of South Korea’s sovereign airspace on Thursday, a day before Seoul announced a visit by the U.S. defense chief next week.

According to Seoul's Joint Chiefs of Staff on Friday, the Chinese warplanes entered the Korea Air Defense Identification Zone or KADIZ at 10:30 and 11:10 a.m. respectively the previous day from an area southwest of Ieo Islet, and left the zone at around noon. 

One of the two jets reentered KADIZ at 3 p.m. and stayed for about 30 minutes but neither of them violated South Korean airspace. 

The area in question is an overlapping air defense identification zone between South Korea and China. The incursion prompted the South Korean military to scramble its warplanes to the scene including the F-15K.

The Chinese fly-by came just before the Pentagon announced Defense Secretary Lloyd Austin will visit Seoul next week. The flight is seen by some as Beijing trying to flex its presence in the region.