North Korean leader Kim Jong Un speaks during an enlarged meeting of the Central Military Commission of the Workers' Party of Korea Thomson Reuters SEOUL (Reuters) - North Korea ramped up its threatening language against the United States on Friday, days before the start of annual joint U.S.-South Korean military exercises that often trigger an angry response from Pyongyang.

North Korea regularly protests the annual exercises, which it calls a rehearsal for war, and has recently stepped up its own air, sea and ground military exercises, amid a period of increased tension between the rival Koreas.

"The DPRK will wage a merciless sacred war against the U.S. now that the latter has chosen confrontation," the country's official KCNA news agency said, quoting from an article in the ruling Workers' Party newspaper, the Rodong Sinmum.

DPRK is short for Democratic People's Republic of Korea, the country's official name.

"Nuclear weapons are not a monopoly of the U.S.," the article said. "The U.S. is seriously mistaken if it thinks its mainland is safe."

North Korea frequently makes such threats against the United States and South Korea, which said on Tuesday the two would begin eight weeks of joint military drills from March 2.

On Friday it said the United States was "much upset by the fact that there may be a sign of detente on the Korean peninsula, thanks to the DPRK's initiative and efforts to achieve peace this year".

However, overtures for dialogue by both Koreas in recent months have stalled, with Pyongyang recently describing inter-Korean relations as "inching close to a catastrophe."

(Reporting by Tony Munroe; Editing by Clarence Fernandez)