North Korea has fired two missiles into the sea off its eastern coast, its fifth such launch in recent weeks.
The missiles are thought to be short-range ballistic missiles, South Korea’s military says.
The latest launch comes shortly after US President Donald Trump said he had received a “very beautiful letter” from North Korean leader Kim Jong Un.
Mr Trump said Mr Kim was unhappy with the current US-South Korea joint military exercises.
North Korea has fired a series of missiles and rockets since Kim and Trump agreed at a June 30 meeting to revive stalled denuclearisation talks.
A US official said that at least one projectile was launched and that it appeared to be similar to previous short-range missiles fired by Pyongyang.