North Korea has reportedly fired at least one missile into the Sea of Japan.
The South Korean Joint Chiefs of Staff reportedly confirmed the incident to the Yonhap News Agency, but have yet to provide further details.
Yonhap says it is not yet known how many were fired and where from.
It comes hot on the heels of two other missiles being fired from North Korea's eastern coastal city of Wonsan into the sea last week.
It was the first time it had fired any missiles for three months, having carried out 13 missile tests last year.
Pyongyang warned at the start of the year that it was developing a "new strategic weapon", which would be unveiled in the near future.
Experts believe leader Kim Jong-Un could be referring to an advanced type of intercontinental ballistic missile (ICBM), or a submarine-launched ballistic missile (SLBM).
The dictator accused US President Donald Trump's regime of making "gangster-like demands" and maintaining a "hostile policy".
Kim also said there were no grounds for North Korea to be bound any longer by a self-declared halt on testing nuclear bombs and intercontinental ballistic missiles (ICBM).
This was imposed following talks between Kim and Trump, but satellite images have suggested Pyongyang has continued work on its nuclear programmes.
He pledged to continue bolstering his country's nuclear deterrent but said the "scope and depth" of that deterrent will be "properly co-ordinated depending on" the attitude of the US.
He signalled there was still room for dialogue with the United States.
"The world will witness a new strategic weapon to be possessed by the DPRK in the near future," Kim said, using the initials for North Korea's official name - the Democratic People's Republic of Korea.
He added: "We will reliably put on constant alert the powerful nuclear deterrent capable of containing the nuclear threats from the US and guaranteeing our long-term security."
