SEOUL—Kim Jong Un’s sister warned that the U.S. should avoid causing a stink with North Korea if the two countries are to enjoy a peaceful relationship, as a pair of top Biden administration officials traveled to the region.

In a Tuesday state-media report, Kim Yo Jong, the younger sister of the North Korean dictator, railed against combined military exercises between the U.S. and South Korea that began last week. The trainings have for years been scaled-down affairs, having moved to computer simulations. But the Kim Jong Un regime has long been irked by the exercises, choosing to view them as U.S. hostilities.