North Korea conducted a ground test of a submarine-launched ballistic missile last week, a U.S. news report said Tuesday, a move that, if confirmed, would add to a series of provocative acts Pyongyang has undertaken in defiance of international pressure.

The March 16 test involved a "pop-up" or "ejection test" of the KN-11 missile from a canister ashore at the Sinpo shipyard on the North's east coast, where the missile is being developed along with the Gorae-class missile-firing submarine, the Washington Free Beacon reported, citing unidentified officials.

Cmdr. Bill Urban, a Pentagon spokesman, declined to comment on the report, citing intelligence matters.

State Department spokesman John Kirby also said he's seen the report, but cannot confirm its veracity.

It was the latest in a series of SLBM tests the North has conducted since May, when Pyongyang claimed it successfully carried out an SLBM test underwater. The regime has since carried out SLBM ejection tests on Nov. 28 and Dec. 21, but they were unsuccessful, according to officials.

The latest test is the first since the U.N. Security Council adopted a new sanctions resolution in response to Pyongyang's fourth nuclear test in January and its long-range rocket launch in February. Like previous resolutions, the resolution also bans Pyongyang from all ballistic missile activity.

The North's SLBM capability, if fully developed, would pose a serious threat because of its mobile nature. But experts say that an "ejection" test is usually conducted in an early stage of developing SLBM capabilities, and Pyongyang is believed to be still many years away from developing an SLBM.

In recent weeks, the North has carried out a series of missile launches in defiance of the U.N. resolution and in a gesture of displeasure over annual joint military exercises between the South and the U.S., which Pyongyang has long branded as a rehearsal for invasion.

Last week, the North also fired two medium-range Rodong missiles, prompting the U.N. Security Council to hold an emergency meeting and issue a statement condemning the firings as a violation of Security Council resolutions.

North Korean leader Kim Jong-un has also threatened to conduct yet another nuclear test and more long-range rocket launches. South Korea said the communist nation is believed to be ready to carry out another nuclear test at any time.

Asked for comment on the possibility of a nuclear test, Kirby said the U.S. is "mindful of the regime's desire to pursue tests like this," but declined to speak to intelligence matters. He added that such a test would be a violation of U.N. resolutions.

"If you're asking me if they were to conduct another test, would it be a violation? Absolutely it would be. And then we would do, as we've done before, take it up inside the U.N.," he said. (Yonhap)