North Korea recently conducted a third test of a new submarine-launched ballistic missile (SLBM) that is part of Pyongyang’s expanding nuclear arsenal, according to American defense officials.

The underwater ejection test of what the Pentagon is calling the KN-11 missile took place April 22 from an underwater test platform near the North Korean coastal city of Sinpo, located on the southeastern coast of the country about 100 miles from the Demilitarized Zone separating it from South Korea.

Doevelpment of the new missile, first disclosed by the Washington Free Beacon, is being carried out at the North’s Sinpo South Shipyard.

The ejection test, which was gauged to have been successful by U.S. intelligence agencies, is the third known test of the new submarine missile, indicating the missile program is a high-priority for the communist regime of Kim Jong Un.

Pentagon spokesman Lt. Col. Jeffrey Pool declined to comment, suggesting details of the test are classified.

Current and former national security officials criticized the Obama administration for not doing more to counter the North Korean nuclear threat to the United States.

"This missile, along with the KN-08, happened on Obama’s watch and nothing has been done," said a U.S. intelligence official critical of the Obama administration.

"By utterly ignoring North Korea's growing missile threats, Obama has allowed the threat of rogue state proliferators to fall out of the center of the national political debate," said John Bolton, former U.S. ambassador to the United Nations. "This is a potential tragedy for the country."

Retired Air Force Lt. Gen. Thomas McInerney said North Korea’s development of the KN-08 and the emerging SLBM present "threats to the continental United States and have been developed under the Obama administration’s leadership."

"Leading from behind is a failed strategy as evidenced by this very dangerous strategic threat to the continental United States of nuclear attack by a very unstable North Korean government," he said.

Allowing Iran to become a nuclear weapons power in 15 years under the Obama’s administration’s propose Iran nuclear deal "puts the United States in the most dangerous threat of nuclear attack since the height of the Cold War but from multiple threats—North Korea, China, Russia, and Iran," McInerney said.

Earlier tests of the KN-11 took place Jan. 23 from a sea-based platform—not a submarine—and another ejection test, in which a missile ejects from a launch system but does not go into flight, from a land-based static platform in October.

Details of the missile program remain classified. Adm. Cecil D. Haney, commander of the Strategic Command, was the first official to confirm the SLBM program in Senate testimony March 19.

The submarine that will be used for North Korea’s underwater-launch missile is not known. Analysts suspect the submarine will be a refurbished Soviet-era Golf II-class submarine that can fire three missiles from its conning tower, or an indigenous missile-firing submarine copied from Russian or Chinese designs. North Korea obtained several Golf-class submarines as scrap metal in the 1990s.

Intelligence analysts said the three tests are an indication of the high priority being placed on developing an underwater nuclear strike capability by Pyongyang.

Joseph DeTrani, former director of the National Counterproliferation Center, a U.S. intelligence agency, said North Korea continues to upgrade its nuclear and missile capabilities in violation of numerous U.N. Security Council resolutions.

"Reported developments with the ICBM-road mobile KN-08 are of immediate concern, as are reports that North Korea is pursuing the development of a SLBM capability," he said.

Former Defense Intelligence Agency official Bruce Bechtol, Jr., said North Korea is developing an SLBM as part of a plan to have missiles capable of reaching the United States and to have missiles that will be difficult to locate for U.S. warning systems.

"With an SLBM they get both," said Bechtol, a North Korea expert. "The submarine can get the platform to launch the missile within range of the continental United States, Alaska, or Hawaii. Thus, once operational, this immediately brings key nodes in the United States within range of what would likely be a nuclear armed missile."

Bechtol said SLBMs provide a key alternative to North Korea’s other new strategic system, the land-based and mobile KN-08.

"This means that, once these two systems go operational, it potentially gives North Korea a dual threat for attacking the United States with nuclear or chemical weapons—a threat generated from difficult to detect mobile platforms on both land and sea," he said.

A month after the November test, the United States, South Korea, and Japan signed a formal intelligence-sharing agreement to better inform each state about the SLBM program and other North Korean threats.

The new missile, when deployed, will join a series of strategic nuclear delivery vehicles available to the North Korean military. The Korean People’s Army currently has long-range Taepodong missiles and road-mobile KN-08 ICBMs capable of delivering nuclear bombs. North Korea has about 40 IL-28 bombers based at Uiju, near the Chinese border, and at Changjun in the central part of the country.

Disclosure of the SLBM ejection test comes as China recently disclosed that it estimates Pyongyang has an arsenal of up to 20 nuclear warheads.

Siegfried Hecker, a Stanford University professor and former director of the Los Alamos National Laboratory, disclosed the 20-warhead North Korean arsenal after taking part in a meeting with Chinese nuclear specialists in February. Hecker said he is concerned by the figure since it represents a "nuclear arsenal."

The Chinese also believe Pyongyang has the capability of producing quantities of weapons-grade uranium that would allow to double its arsenal by next year.

The North Korean nuclear warhead arsenal, when combined with its missile forces, poses a direct threat to the United States, senior U.S. military officials said last month.

Adm. William Gortney, commander of the U.S. Northern Command, told reporters April 7 that U.S. intelligence agencies have formally assessed that North Korea is capable of making a nuclear warhead small enough to fit on a missile.

North Korea’s KN-08 is also a major worry because the mobile missile is difficult to track and can be fired with little warning.

"Our assessment is that they have the ability to put a nuclear weapon on a KN-08 and shoot it at the homeland," Gortney said, adding that the missile has not been flight-tested.

Gortney, who is in charge of defending the United States from missile attacks, added that "we're very concerned about the mobile nature of the KN-08, that we would lose our ability to get the indication that something might occur, and then, of course, the particular nature of the regime that's there."

Little is known about the nature of the KN-11. However, State Department documents disclosed by Wikileaks revealed that North Korea obtained a Russian SS-N-6 submarine-launched ballistic missile several years ago that became the basis for Pyongyang’s intermediate-range Musudan missile.

Missile Defense Agency Director Vice Adm. James Syring voiced alarm at the impact of North Korean missile development and sharp budget cuts for American missile defenses.

Syring told the House Armed Services Strategic Forces Subcommittee March 19 that if budget cuts continue "you're starting to jeopardize our future capability … to defend the homeland with the development and testing that I've seen going on with North Korea very specifically, and the pace in the progress that they're making."

Unless improvements are made in missile defenses, "I'm in serious jeopardy of … going to the Northern commander and advising him the system is overmatched."

Meanwhile, North Korea announced April 30 that it plans to enhance its nuclear power infrastructure following the announcement that the United State and South Korea had reached a nuclear energy treaty.

"This is a dangerous criminal move which will escalate tension on the Korean Peninsula and spark off nuclear proliferation and a nuclear arms race in Northeast Asia," North Korea’s official KCNA news agency said in a statement.

As a result, Pyongyang vowed to "further bolster up its self-defensive nuclear deterrence for defending the dignity of the nation, its sovereignty, and global peace and security," the statement said.

In a related development, a North Korea expert who studied in Pyongyang said recent reports indicate North Korea is preparing to conduct a satellite launch in the near future.

Alexandre Mansourov, visiting scholar at the John Hopkins School of Advanced International Studies, said a close reading of activities by Kim Jong Un and space-related stories in state-controlled media indicate a launch could be carried out in mid-September or early October.

"The upcoming space launch, in violation of the existing U.N. Security Council resolutions, will demonstrate the Kim regime's unswerving determination to pursue a robust space program despite international approbation and the missile test ban, will test the limits of Beijing's patience and Moscow's rapprochement with Pyongyang, and may compel Washington to expedite the deployment of missile defenses in the region, while straining U.S. relations with its allies ROK and Japan," Mansourov said.