Residents of Japanese coastal towns are holding evacuation drills as North Korea warned Sunday that the upcoming US-South Korea military exercises are "reckless behavior driving the situation into the uncontrollable phase of a nuclear war."

Nearly 130 people took part in the drill in Kotoura, which has a population of 18,000, a town official said. Reuters reports that for 10 minutes, people ducked down covering their heads with their arms. Many of those taking part said they were worried. North Korea has in the past threatened to attack Japan, a staunch U.S. ally and host to U.S. military bases.

As sirens blared from speakers in the town of Kotoura, children playing soccer outside ran to take shelter in a school, along with their parents and their team coach.

"I've been concerned every day that something might fall or a missile could fall in an unexpected place due to North Korea's missile capabilities," said the coach, Akira Hamakawa, 38.

As a reminder, Japan is the only country in the world to be attacked with nuclear weapons, and so perhaps the threats from North Korea today are a little closer to heart than for many around the world.

Following North Korean leader Kim Jong Un's statement last week that he would "watch a little more the foolish and stupid conduct of the Yankees," as US-South Korean military exercises begin, CNN reports that Pyongyang also declared that its army can target the United States anytime, and neither Guam, Hawaii nor the US mainland can "dodge the merciless strike."

The messages in Rodong Sinmun, the official government newspaper, come a day before the US starts the Ulchi Freedom Guardian military exercises with South Korea.

"The Trump group's declaration of the reckless nuclear war exercises against the DPRK ... is a reckless behavior driving the situation into the uncontrollable phase of a nuclear war," Rodong Sinmun said, using the acronym for Democratic People's Republic of Korea, the nation's official name. It described North Korea as the "strongest possessor" of intercontinental ballistic missiles capable of striking the US mainland from anywhere. "The Korean People's Army is keeping a high alert, fully ready to contain the enemies. It will take resolute steps the moment even a slight sign of the preventive war is spotted," it said.

China has urged both Washington and Pyongyang to tone down the rhetoric, warning via the government's mouthpiece Global Times...

"The drill will definitely provoke Pyongyang more, and Pyongyang is expected to make a more radical response," it said in an editorial. "If South Korea really wants no war on the Korean Peninsula, it should try to stop this military exercise."

Kim's threats come after both US Secretary of State Rex Tillerson and Secretary of Defense James Mattis said last week that the US was keeping military options on the table in dealing with North Korea.