North Korean leader Kim Jong Un said a U.S.-South Korea joint military exercise could "ignite a war" and called for the rapid expansion of Pyongyang's nuclear capabilities.

Kim Yo Jong, a senior official on the State Affairs Commission, called South Korean President Lee Jae-myung’s push for improved ties a “pipe dream,” according to a statement published by the Korean Central News Agency. She accused Lee or trying to create an “amicable image” while hosting a large-scale military exercise with the United States.

The powerful sister of North Korean leader Kim Jong Un on Thursday dismissed South Korean claims the North is removing some of its loudspeakers along the inter-Korean border, mocking the government in Seoul for clinging to hopes of renewed diplomacy between the war-divided rivals.