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

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

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

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

According to Japan's Defense Ministry, the missiles flew about 500 kilometers and reached a maximum altitude of around 550 kilometers.

Japanese Senior Vice Defence Minister Toshiro Ino said Pyongyang's missiles test "threatens the peace and security of our country, this region, and the international community, and it is absolutely unacceptable."

Sunday's launch came days after the DPRK 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."

Despite heavy international sanctions over its weapons programs, Pyongyang has built up an arsenal of intercontinental ballistic missiles (ICBMs).

North Korean leader Kim Jong Un has placed strategic priority on developing solid-fuel engines for more advanced missiles.

Kim said this year that he wants the DPRK to have the world's most powerful nuclear force and declared his country an "irreversible" nuclear state.

The wishlist he revealed last year included solid-fuel ICBMs that could be launched from land or submarines.

The DPRK's policy direction for next year will be laid out at a key party meeting later this month, and the official Korean Central News Agency earlier reported Kim saying that 2023 would be a "historic year".

In past years, Kim had delivered a speech every January 1 but has recently dropped the tradition in favor of making announcements at the year-end plenary meeting.

The DPRK has conducted dozens of missile tests this year, including multiple launches of ICBMs with potential range to the US mainland and an intermediate-range missile flown over Japan.

The launches came in response to the expansion of the allies' combined military exercises, which DPRK insists are rehearsals for an invasion.

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