North Korea fired two short-range ballistic missiles Friday, Seoul's military said, the latest in a recent flurry of sanctions-busting weapons tests.

It has been a year of unprecedented tests by the North, including the launch of its most advanced intercontinental ballistic missile last month, the test of what Pyongyang says was a new rocket engine last week, and claims this week it has developed new capabilities to take images from space.

"Our military spotted two short-range ballistic missiles launched by North Korea into the East Sea from the Sunan area of Pyongyang at around 16:32 (0732 GMT) today," South Korea's Joint Chiefs of Staff said, referring to the body of water also known as the Sea of Japan.

"Our military maintains a full readiness posture while closely cooperating with the US while strengthening surveillance and vigilance."

The United States and South Korea have warned for months that Pyongyang is preparing to conduct its seventh nuclear test.

The two countries held a joint air drill on Tuesday, and deployed a US B-52H strategic bomber to the Korean peninsula, according to the South Korean Joint Chiefs of Staff.

The long-range heavy bomber was part of an exercise that included the US and South Korea's most advanced jets -- including the F-22 and the F-35 stealth fighters.

Friday's launch came hours after the White House said Pyongyang had delivered arms to the Russian private military group Wagner.

Disclosing the delivery on Thursday US time, the White House called Wagner a "rival" for power to the defense and other ministries in the Kremlin.

- 'Putin's chef' -

The Wagner group is controlled by Yevgeny Prigozhin, a businessman once called "Putin's chef" for his work catering dinners for the powerful leader before and after he became the Russian president.

In a statement carried by the Korean Central News Agency, the North Korean foreign ministry denied conducting any arms transaction with Russia, saying the story was "cooked up by some dishonest forces for different purposes".

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

Last week, 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".

All its known ICBMs are liquid-fueled, and North Korean leader Kim Jong Un has placed strategic priority on developing solid-fuel engines for more advanced missiles.

His powerful sister also insisted earlier this week that the North had developed advanced technologies to take images from space using a spy satellite.

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 wish list 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.

(AFP)

This photo provided by the North Korean government, shows what it says a test of a rocket with the test satellite at the Sohae Satellite Launching Ground in North Korea Sunday, Dec. 18, 2022. (AP)

North Korea fires two ballistic missiles: Seoul's military