According to the US military, North Korea has fired three short-range ballistic missiles.
The missiles were launched from a site in the North Korean province of Gangwon and flew for about 150 miles, officials in South Korea said.
Since firing an intercontinental ballistic weapon last month, North Korea has threatened to aim missiles at the US Pacific territory of Guam.
However, this latest test did not threaten the US or Guam, the US military said.
North Korean missile tests often come in response to South Korean military exercises involving the US.
Thousands of US and South Korean troops are currently taking part in joint military drills, which are mainly largely computer-simulated exercises.
The projectiles were launched at 06:49 on August 26, South Korea’s defense ministry said.
The US military initially reported that two of the missiles had failed but, according to its later assessment, one appears to have blown up almost immediately while two flew about 155 miles in a north-easterly direction.
The launches were spread over a period of 30 minutes, an official said.
The South Korean defense ministry said: “The military is keeping a tight surveillance over the North to cope with further provocations.”