North Korea 'fires two ballistic missiles' into Sea of Japan, South Korean military reports

North Korea has fired two short-range ballistic missile into the Sea of Japan, South Korea's military has said.

The two missiles were fired at around 5:20 am on Wednesday from North Hwanghae Province and hit waters northeast of the port city of Wonsan off the country's east coast, according to The Joint Chief of Staff (JCS), Yonhap news agency reports.

Sources told the South Korean agency the missiles flew around 500 kilometers.

The JCS said: "The military is keeping close tabs on the situation and prepared to deal with any North Korean provocations."

North Korean leader Kim Jong-un, talking with scientists and technicians involved in the research of nuclear weapons, at an undisclosed location

The announcement comes after Kim Jong-un said on Tuesday North Korea now possesses nuclear warheads small enough to fit on ballistic missiles.

The kingdom made the claim by publishing photos on the front page of its ruling party newspaper that show the country's leader standing beside what it said was miniaturised nuclear warhead during a meeting with his top scientists. 

The Rodong Sinmun newspaper photos showed Kim and the scientists standing by what outside analysts say appears to be the model warhead - a small, silverish globe presented on a low table in a hangar with a ballistic missile or a model ballistic missile in the background. 

This is the second time North Korea have launched missiles into the Sea of Japan in just one week.

On 3 March the country fired short-range missiles into the Sea of Japan, just hours after the UN Security Council voted in favour of sanctions against the regime.

The UN passed the toughest sanctions in two decades against North Korea after it carried out a nuclear bomb test and launched a long-range missile, causing security tensions to increase.

As a result of the sanctions, all cargo going in and out of the country will be inspected, while 16 more people and 12 organisations have been blacklisted.

North Korea has also threatened to turn Washington and Seaol into "flames and ashes" and warned of pre-emptive nuclear strikes after the United States and South Korea began holding their biggest-ever war games, which will go on until the end of April.