North Korea on Wednesday condemned the joint naval drills by South Korea and the U.S. saying that the exercises were an “advance preparation for mounting a preemptive attack.” Seoul and Washington held the drills last week in the East Sea in a show of force to the isolated nation’s fifth nuclear test.

“If the aggressors and provocateurs dare mount a preemptive attack on the DPRK [Democratic People’s Republic of Korea], they will not be able to escape a merciless, nuclear retaliatory strike of justice,” North Korean daily Rodong Sinmun said in a commentary, according to South Korea's Yonhap News Agency.

The joint drills involved training for precision strikes on important targets on the ground. This was the first time when the U.S. and South Korean vessels operated together in waters so close to the North’s east coast, a U.S. Navy official told CNN last Wednesday.

Meanwhile, South Korea is reportedly planning to develop or buy a laser air defense system to bring down North Korea’s drones. Currently, the drones sent by the Kim Jong Un-led country can reportedly be brought down with surface-to-air missiles or anti-aircraft guns. The South Korean military found five instances where North Korean drones crossed the military demarcation line in August, Yonhap reported last Wednesday.

North Korea was condemned by several nations for its latest nuclear test on Sept. 9. Pyongyang has actively conducted nuclear and missile tests, upsetting South Korea as well as other world powers including the U.S., Japan, Russia and even China — the North’s only major diplomatic partner.