(CNN) The Pentagon will conduct two major high-stakes tests in May of its ability to shoot down missiles launched out of North Korea.

The long-scheduled tests in the Pacific are part of the US military's overall ballistic missile defense program to defend against North Korean or Iranian threats -- but are, for now at least, aimed at ensuring the US can defend against a threat from North Korea, US defense officials said.

One of the actions will involve test-firing an improved Standard Missile off a Navy ship, a defense official said. The tests are taking place over the Pacific because that's where the test ranges are large enough to accommodate them.

The upgraded missile has only been tested once before. The new version has an improved booster and warhead. That means the missile could fire at longer ranges, presumably farther from the North Korean coastline, and have a greater chance of hitting the threatening incoming missile.

The program has been in development with Japan and is aimed at shooting down intermediate-range North Korean missiles that pose a threat to the US ally.

A separate critical test in the Pacific region, to be held at the end of May, will examine the ability of the US to shoot down a future North Korean intercontinental ballistic missile that could threaten the US.

That test involves long-range ground-based interceptor missiles based in Alaska and California. That program has also been in existence for over a decade, but only about half the tests have been successful, according to the Defense Department.

In the most recent Pentagon report on weapons testing across the department, the long-range system was criticized. The report said it "demonstrates a limited capability to defend the US homeland from small numbers of simple intermediate-range or intercontinental ballistic missile threats launched from North Korea or Iran."

The report went on to say that the Pentagon continued to discover new failures during testing.

In the upcoming test, a missile will be launched from the Vandenberg Air Force Base in California and attempt to intercept a simulated missile over the Pacific Ocean.

As part of a broader National Security Council review of options for dealing with North Korea, the Pentagon has been considering its military options for more than a month in case the White House were to decide to take such action, a defense official said. The NSC effort is also looking at diplomatic and economic options.

The official pointed out the recent engagement with the Chinese, and the stronger language calling for more Chinese pressure on North Korea, is the most immediate impact of that review.

The review of military options is essentially "due diligence," the official said. Top military and civilian Pentagon officials are "thinking through every course of action."

That also involves updating any analysis on the latest thinking of how North Korea might militarily react if the US were to take military steps.

The official emphasized that all of the ongoing work doesn't change the administration -- and Pentagon's -- emphasis on the need for a peaceful diplomatic solution.

The official was adamant that the US is currently not anticipating pre-emptive military action against North Korea. Standard policy -- which calls for shooting down of a North Korean missile after launch if the trajectory is deemed to threaten South Korea, Japan or the US -- remains in place.

The review also is aimed at ensuring necessary military assets are properly situated if there is a need for military action. Multiple US officials said all current anti-missile ships and other ground-based interceptors in Alaska are available.

Even as the military options are reviewed and updated, Defense Secretary James Mattis is also underscoring the need for a non-military solution.

"You're aware that the leader of North Korea again recklessly tried to provoke something by launching a missile," he recently told reporters. "It was not an intercontinental ballistic missile, it failed on launch, and it shows why we're working so closely right now with the Chinese."

Both countries are trying "to get this under control and aim for a denuclearized Korean Peninsula," he said. "China and the United States and South Korea, Japan, we all share that same interest."