North Korea conducted large-scale artillery exercises on Tuesday to coincide with the 85th anniversary of its army's foundation, South Korea's Yonhap News Agency reported.

Citing an unidentified South Korean government source, Yonhap reported that there were signs North Korea's military was carrying out large-scale, live-fire drills in areas around the east coast city of Wonsan.

South Korea's defense ministry could not immediately confirm the report, according to Reuters.

North Korea warned that the United States will have to choose between political and military surrender, according to the Yonhap report.

"If the U.S. and warmongers run amok with a reckless preemptive strike, we will stage the most brutal punishment of a preemptive attack in the sky and land as well as at sea and from underwater without any warning or prior notice," according to Rodong Sinmun, spokesman of the ruling Workers' Party of Korea.