SEOUL/TOKYO: North Korea fired two short-range ballistic missiles into the sea on Thursday in the direction of Japan, after the return of a U.S. aircraft carrier to the region and a U.N. Security Council meeting in response to the North's recent launches.

The missile launch was the sixth in 12 days and the first since North Korea fired an intermediate-range missile (IRBM) over Japan on Tuesday, which prompted joint South Korean and U.S. missile drills during which one weapon crashed and burned.

The launch was reported by South Korea's Joint Chiefs of Staff and the Japanese government.

"This is the sixth time in the short period, just counting the ones from the end of September," Japanese Prime Minister Fumio Kishida told reporters. "This absolutely cannot be tolerated."

The launch came about an hour after North Korea condemned the United States for talking to the United Nations Security Council about Pyongyang's "just counteraction measures of the Korean People's Army on south Korea-U.S. joint drills," suggesting its missile tests are a reaction to the allied military moves.

In a statement released by the reclusive nation's foreign ministry, North Korea also condemned Washington for repositioning a U.S. aircraft carrier off the Korean peninsula, saying it posed a serious threat to the stability of the situation.

The USS Ronald Reagan and its strike group of accompanying warships was abruptly redeployed in response to North Korea's IRBM launch over Japan.

The United States condemned Thursday's launch, a State Department spokesperson said, calling it a violation of the United Nations Security Council resolutions and a threat to regional neighbours and the international community. 

The spokesperson, however, added that Washington is committed to a diplomatic approach and called on the North to engage in dialogue.

The United States accused China and Russia on Wednesday of enabling North Korean leader Kim Jong Un by blocking attempts to strengthen U.N. Security Council sanctions on Pyongyang over its nuclear weapons and ballistic missile programs.

South Korean President Yoon Suk-yeol, who is due to speak to Kishida by phone on Thursday, told reporters that his country will ensure its security through its alliance with the United States and cooperation with Japan.

He said the U.S. carrier had entered waters off South Korea late on Wednesday.

Yoon's national security council warned that North Korea would face a strong international response over the tests.

Tokyo lodged a "vehement protest" with North Korea over Thursday's launches through delegations in Beijing, Japanese Defense Minister Yasukazu Hamada said.

The first missile on Thursday likely flew to an altitude of about 100 km and a range of 350 km, while the second one had an estimated altitude of 50 kilometers (31.07 miles) and covered 800 km, likely flying in an irregular trajectory, he said.

Many of North Korea's most recent short-range ballistic missiles (SRBMs) are designed to fly on a lower, depressed trajectory and potentially manoeuvre, complicating efforts to detect and intercept them.

"North Korea has relentlessly and unilaterally escalated its provocation especially since the beginning of this year," Hamada told reporters.

South Korea's JCS said the missiles were launched from near the North Korean capital of Pyongyang.

North Korea has launched about 40 missiles this year. Its record schedule began in January with the launch of a new "hypersonic missile," and went on to include long-range cruise missiles; SRBMs fired from rail cars, airports, and a submarine; its first intercontinental ballistic missile (ICBM) launches since 2017; and the IRBM shot over Japan. 

It also appears ready to conduct a nuclear test for the first time since 2017, according to officials in Seoul and Washington.

The United States and its allies have stepped up displays of military force in the region, but there appears to be little prospect of further international sanctions from the U.N. Security Council, which has already passed resolutions banning the North's missile and nuclear development.

China's deputy U.N. ambassador, Geng Shuang, said the Security Council needed to play a constructive role "instead of relying solely on strong rhetoric or pressure."

In May, China and Russia vetoed a U.S.-led push to impose more U.N. sanctions on North Korea over its renewed ballistic missile launches, publicly splitting the Security Council for the first time since it started punishing Pyongyang with sanctions in 2006.