SEOUL, South Korea (AFP) — 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 a.m. to 12:05 p.m. into the East Sea, referring to the body of water also known as the Sea of Japan, it said.

"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.

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."

Despite heavy international sanctions over its weapons programs, Pyongyang has built up an arsenal of ICBMs.

All its known ICBMs are liquid-fueled, however, and 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 North Korea 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 latest motor test was a step towards that goal, but it is not clear how far North Korea has come in the development of such a missile, analysts said.