As South Korea and the United States prepare for their annual military exercises, North Korea is warning of “indiscriminate” nuclear strikes targeting the two countries.

In a statement, Pyongyang said it ordered “preemptive nuclear strikes of justice,” threats that experts say is not uncommon for the country, but not realistic based on their capabilities. North Korea sees the military drill as rehearsal for an invasion and this year’s exercises, with 300,000 South Korean troops and 15,000 U.S. personnel participating, will be the largest ever.

A spokesman for South Korea’s defense said if North Korea “ignores our warning and makes provocations, our military will firmly and mercilessly respond to it.” Last week, the U.N. passed its toughest sanctions in 20 years against North Korea after the communist country launched a rocket and held a nuclear test against the sanction’s policies.