North Korea has fired two missiles into the sea, its fifth such launch in recent weeks.
The missiles are thought to be short-range ballistic missiles, South Korea’s military says.
If confirmed, such a test would be a breach of 11 UN security Council resolutions.
The launches come 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.