North Korea fires ballistic missile into waters off east coast

North Korea fired two ballistic missiles Sunday, Seoul's military said, days after Pyongyang announced a successful test of a solid-fuel motor for a new weapons system.

Military tensions on the Korean peninsula have risen sharply this year as Pyongyang has carried out an unprecedented blitz of weapons tests, including the launch of its most advanced intercontinental ballistic missile ever last month.

South Korea's Joint Chiefs of Staff said it detected two ballistic missiles that had been fired from the Tongchang-ri area in North Pyongan province.

The missiles were fired from 11:13 am (0213 GMT) to 12:05 pm into the East Sea, it said, referring to the body of water also known as the Sea of Japan.

"Our military has strengthened surveillance and vigilance while closely cooperating with the United States and maintaining a full readiness posture," the JCS added in a statement.

The missiles flew about 500 kilometres and reached a maximum altitude of around 550 kilometres, according to Japan's defence ministry.

"It threatens the peace and security of our country, this region, and the international community, and it is absolutely unacceptable," said senior vice defence minister Toshiro Ino.

Sunday's launch came days after North Korea tested a "high-thrust solid-fuel motor", with state media describing it as an important test "for the development of another new-type strategic weapon system".