North Korea test fires missiles from submarine amid US, South Korean military drills

North Korea fired at least one missile from a submarine in the Sea of Japan on Sunday, ramping up missile tests ahead of one of the largest joint military exercises between the U.S. and South Korea.

North Korea claimed to have fired two missiles from a submarine in the sea, but South Korean military officials said they only tracked one missile fired from the submarine near the North Korean port city of Sinpo.

The launch comes on the eve of what is expected to be 11 days of joint military exercises between the U.S. and South Korea, dubbed Freedom Shield. North Korean leader Kim Jong Un and those close to him have voiced rising concerns about the close military relationship between the U.S. and South Korea.

The underwater test comes as North Korea also launched a ballistic missile toward the water of the Yellow Sea last week, according to South Korean officials. They said they could not confirm where it landed. That launch followed U.S. and South Korean military exercises earlier last week that included the deployment of a B-52 long range bomber plane. 

The aggression shown by the North Korean military follows a trend of unprecedented missile tests last year. U.S. intelligence agencies concluded last week that North Korea had been timing its missile tests to coincide with joint military exercises between the U.S. and South Korea.

The U.S.-South Korean military operations this week are expected to be the largest exercises in the last five years.