North Korea launched an intercontinental ballistic missile off its east coast on Monday, its first long-range missile test since July, the South Korean military said.

The missile was fired from near Pyongyang, the North’s capital, flying high into space before landing 620 miles to the east in waters between the Korean Peninsula and Japan, South Korean military officials said. As in previous ICBM tests, North Korea launched the missile at a steep angle, apparently so it would not fly over Japan.

South Korean officials said they were analyzing the launch to determine what type of ICBM it was.

North Korea last conducted an ICBM test on July 12, when it tested its Hwasong-18 missile. The Hwasong-18, first launched in April, is the North’s first ICBM to use solid fuel. That makes it easier to move and launch quickly — and therefore more dangerous — than older versions that relied on liquid fuel.

The United States and its allies, particularly South Korea and Japan, have become increasingly concerned about North Korea’s frequent missile tests under its leader, Kim Jong-un, because the country ​claims to have​ developed a new, small nuclear warhead that it can mount on its various missiles.

“Any nuclear attack by North Korea against the United States or its allies is unacceptable and will result in the end of the Kim regime,” senior American and South Korean officials, known as the Nuclear Consultative Group, said in a joint statement on ​Saturday after meeting in Washington.

The Nuclear Consultative Group was established in April, when President Biden and his South Korean counterpart, Yoon Suk Yeol, agreed to deepen the two allies’ discussions on how to deter and respond to a nuclear attack from North Korea.

The United States has also highlighted its commitment to defend South Korea by expanding joint military drills, inviting South Korean officials to the test launch of an American ICBM and sending U.S. aircraft carriers, strategic bombers and a nuclear missile submarine to visit the ally. The U.S.S. Missouri, a Virginia-class nuclear-powered attack submarine, arrived at Busan, a South Korean port city​, on Sunday.

In a statement on the same day, North Korea characterized the two allies’ recent moves as an attempt “to make the use of nuclear weapons against the D.P.R.K. a fait accompli in case of emergency.” D.P.R.K. stands for the Democratic People’s Republic of Korea, the North’s formal name.

“It is none other than the U.S. and its vassal forces that unilaterally escalate the military tension in the Korean Peninsula by words or deeds,” said the statement, attributed to a spokesman for the North Korean Ministry of National Defense. “Every moment, the crisis of nuclear conflict in the Korean Peninsula is turning into the issue of a point of time, not the issue of possibility.”

​North Korea has often issued such dire warnings to justify the development of its arsenal and to help consolidate domestic unity around Mr. Kim’s leadership in the face of international sanctions.

Mr. Kim has doubled down on​ expanding the North’s missile and nuclear weapons ​capabilities since his direct negotiations with President Donald J. Trump collapsed in 2019. Last year, North Korea carried out 37 missile tests, some of which involved multiple missiles. It has conducted 24 tests this year, including a short-range ballistic missile launched off its east coast on Sunday night.

In September, ​North Korea said that its first submarine capable of launching nuclear missiles had gone into operation, giving it a new, harder-to-detect means of launching a nuclear strike. Two months later, it placed its first military reconnaissance satellite into orbit.

The new short-range ballistic missiles the North has tested since 2019 all used solid fuel. It conducted ground tests of a new solid-fuel rocket for its intermediate-range ballistic missiles in November.

Under multiple United Nations Security Council resolutions, North Korea is forbidden to develop nuclear weapons or test ballistic missile technologies. But Russia and China have vetoed attempts to impose new sanctions on the North over its recent wave of missile​ tests.

Analysts say Russia’s invasion of Ukraine and rising tensions between Washington and Beijing have given North Korea ​the opportunity to strengthen its ​ties with old Cold War allies and conduct ballistic missile tests with impunity.