SEOUL, Dec 23 (AFP) - North Korea fired two ballistic missiles towards the sea off its east coast on Friday, the South Korean military said, the latest in an unprecedented number of missile tests this year.

Coming only days after two other missiles were launched and just after allegations were made on Thursday the country is shipping munitions to Russian forces in Ukraine, the incident shows that North Korea does not intend to stop the provocative actions its neighbours say are destabilising regional security.

South Korea's Joint Chiefs of Staff (JCS) said the missiles flew 350 km (217.5 miles) and 250 km, respectively, after being fired at around 16:30 p.m. (0730 GMT) from the Sunan area of the North Korean capital Pyongyang. Japan's coast guard also reported a suspected ballistic missile launch.

Such launches are a "serious provocation that harms peace and stability" on the Korean peninsula and beyond and a clear violation of U.N. resolutions, the JCS said, urging an immediate halt.

"We will track and monitor developments together with the United States in preparation for additional provocations by North Korea, while maintaining a firm readiness posture based on our ability to overwhelmingly respond to any provocations by North Korea," the JCS said in a statement.

Japan's State Minister of Defence Toshiro Ino said his country has lodged a strong protest to North Korea through diplomatic channels in Beijing.

Japanese Chief Cabinet Secretary Hirokazu Matsuno condemned the latest launch as "absolutely unacceptable."

"North Korea's rapid escalation of provocations in a series of actions threatens the peace and security of Japan's region and the international community," Matsuno told reporters.

The launch comes five days after the isolated country fired two mid-range missiles in what it called an "important" test for the spy satellite programme it intends to complete by April.

The White House said on Thursday that North Korea completed an initial arms delivery of infantry rockets and missiles to a private Russian military company, the Wagner Group, to shore up Russian forces in Ukraine.

Wagner owner Yevgeny Prigozhin denied the assertion as "gossip and speculation".

Pyongyang's foreign ministry on Friday also denied a Japanese media report on munitions shipments to Russia, calling it "groundless".

Tokyo Shimbun reported that North Korea had shipped artillery shells and other munitions to Russia by train last month, with additional shipments expected in coming weeks.

North Korea's foreign ministry said it has never conducted arms transactions with Russia and criticised Washington for giving lethal weapons to Ukraine, with no mention of Wagner.