(CNN) North Korea has lashed out at the US after it conducted joint bomber drills with the South Korean air force, accusing it of reckless provocation.

Pyongyang described the exercise, which involved two B1-B bombers, as a "nuclear bomb-dropping drill" that made nuclear war more likely. North Korean state media described US President Donald Trump as a "warmonger".

The outburst came as the officials said that a controversial US missile defense system was up and running in South Korea -- albeit in a limited capacity. That announcement came a week before presidential elections in South Korea that are expected to bring in a government critical of the Terminal High Altitude Area Defense system, known as THAAD.

JUST WATCHED Trump says nobody is safe from North Korea Replay More Videos ... MUST WATCH Trump says nobody is safe from North Korea 02:20

The latest belligerent statement from Pyongyang was a response to the deployment of two US bombers over the Korean peninsula on Monday -- as part of a joint drill with South Korea and Japan's air forces.

South Korean Defense Ministry spokesman Moon Sang-gyun told a briefing Tuesday that the deployment was part of an effort to "respond to North Korea's nuclear missile threat and to deter North Korea's provocations."