Pyongyang announced it sent a message to Gen. James Thurman, warning the exercises create a situation that could lead to a real war, South Korea's Yonhap news agency said.
The message was relayed by telephone to Thurman by Pak Rim-su, the North Korean military representative at the truce village of Panmunjon.
"If your side ignites a war of aggression by staging the reckless joint military exercises Key Resolve and Foal Eagle again under the cover of 'defensive and annual ones' at this dangerous time, from that moment your fate will be hung by a thread with every hour," said Pak's warning, which was delivered in English.
Key Resolve, scheduled for March, is largely a computer-simulated exercise, but Foal Eagle will involve about 14,000 South Korean and U.S. troops. Most of the U.S. participants are based in countries other than South Korea, Yonhap said.