North Korea fired what appeared to be two short-range ballistic missiles into the East Sea on Thursday, the Joint Chiefs of Staff (JCS) said, an apparent move pressing the United States as Washington prepares to announce a new policy on the North.

The missiles were fired from the North's eastern town of Hamju, South Hamgyong Province, at 7:06 a.m and 7:25 a.m. and flew around 450 kilometers with an altitude of 60 km, the JCS said.

"South Korean and US intelligence authorities are analyzing the projectiles in detail, weighing the possibility that they could be short-range ballistic missiles," a JCS officer said.

North Korea last fired a ballistic missile in March 2020.

It was not immediately known whether the North's leader Kim Jong-un oversaw the firings.

"Our military is maintaining a thorough readiness posture in preparation for additional provocations while closely monitoring related moves," the JCS said in a statement.

The presidential office Cheong Wa Dae convened an emergency National Security Council meeting and expressed "deep concern" over the North's latest projectile launch.

Thursday's launches mark a gradual ratcheting up of tensions by the North as they came four days after the country fired two cruise missiles into the Yellow Sea on Sunday.

The United States brushed off the cruise missile launches as part of "normal testing" not banned under UN sanctions resolutions, with President Joe Biden saying, "nothing much has changed."

But ballistic missile launches constitute a violation of UN Security Council resolutions, though Pyongyang has maintained a self-imposed moratorium on nuclear and long-range missile testing since late 2017.

Washington's reaction to the latest launches was not immediately available.

But the US military said the launches highlights the threat the North poses.

"This activity highlights the threat that North Korea's illicit weapons program poses to its neighbors and the international community," USFK spokesman Col. Lee Peters said. "The US commitment to the defense of the Republic of Korea remains ironclad."

Ballistic missiles have a much longer range than cruise missiles of the same size and move quickly along their flight path. Ballistic missiles are also deemed more threatening, as they are designed to deliver nuclear weapons.

The latest launch also came as the Biden administration was completing its North Korea policy review.

North Korea's First Vice Foreign Minister Choe Son-hui said last week any contact and dialogue with the US can be possible only when Washington rolls back its "hostile policy" toward it.

North Korean leader Kim held three meetings with former US President Donald Trump, but denuclearization talks remain stalled since the collapse of their Hanoi summit in February 2019.

The US is scheduled to hold a security meeting with South Korea and Japan next week to discuss how to deal with issues involving North Korea. (Yonhap)