North Korea fired several cruise missiles off its east coast on Wednesday as South Korea and the United States conducted joint military exercises, the South Korean military said, Reuters reported.

South Korea’s Joint Chiefs of Staff said the missiles were fired at around 10:15 a.m. (01:15 GMT) from South Hamgyeon province.

It was not immediately clear how many shells were fired or what type they were.

The launch came three days after North Korea fired a short-range ballistic missile into the sea off its east coast.

Pyongyang accuses South Korea of ​​joint military exercises with the United States, which will last ten days, as a rehearsal for an invasion of its territory.

South Korea and the US say the drills are purely defensive.

The JCS said in a statement that the military was on high alert and South Korean and US intelligence agencies were investigating the launches.

South Korea’s Yonhap news agency said Wednesday’s launches may have involved strategic cruise missiles.

“Strategic” is usually used to describe weapons that have nuclear capabilities.

North Korea was last known to launch strategic cruise missiles on March 12, when it said it fired two from a submarine.

A U.S. State Department official said it continues to urge North Korea to “refrain from any further destabilizing actions” and reiterated that the U.S. commitment to the defense of South Korea and Japan remains “ironclad.”

North Korea says around 800,000 of its citizens have voluntarily joined or re-enlisted in the national army to fight the United States, the state-run Rodong Sinmun newspaper reported on Saturday.