The U.S. Army and South Korean military responded to North Korea’s launch with their own exercise of missiles, launching them Tuesday into South Korean territorial waters along the country’s eastern coastline, U.S. Pacific Command said in a statement. The launches were directly in response to “North Korea’s destabilizing and unlawful actions,” Pacific Command said.

Earlier Tuesday, North Korea launched a missile that flew higher and remained in the air longer than previous attempts, enough to reach all of Alaska, experts said, in a milestone for North Korea’s weapons program.

Hours after the apparently successful test, intelligence agencies continued to run calculations to determine precisely how the missile, dubbed the Hwasong-14, performed in its maiden flight. But the consensus among missiles experts was that North Korea had demonstrated a capability of striking targets thousands of miles from its coast.

Initial Pentagon assessments said North Korea had tested a “land-based, intermediate-range” missile that landed in the Sea of Japan just under 600 linear miles from its launch point, Panghyon Airfield, near the Chinese border. But government and independent analyses showed the missile traveling in a steep arc that topped out at more than 1,740 vertical miles above the Earth’s surface.

If flown in a more typical trajectory, the missile would have easily traveled 4,000 miles, potentially putting all of Alaska within its range, according to former government officials and independent analysts. A missile that exceeds a range of 3,400 miles is classified as an intercontinental ballistic missile, or ICBM.

“This is a big deal: It’s an ICBM, not a ‘kind of’ ICBM,’” said Jeffrey Lewis, director of the East Asia program at the Center for Nonproliferation Studies. “And there’s no reason to think that this is going to be the maximum range.”

In response to the North’s launch, the U.S. Army used its Army Tactical Missile System and South Korea used its Hyunmoo Missile II, which can be deployed rapidly and provide “deep strike precision capability, Pacific Command said.

The South Korean-U.S. military alliance “remains committed to peace and prosperity on the Korean Peninsula and throughout the Asia-Pacific,” Pacific Command said. “The U.S. commitment to the defense of the [Republic of Korea] in the face of threats is ironclad.”

The Army describes the missiles it used as long-range, all-weather guided missiles. They are designed to be precise in nature, and can be used beyond the range of artillery and rockets.

The U.S. missile system can be used to take out ground combat units, surface-to-surface missile units, air-defense units, helicopter re-arming and refueling systems or communications sites, according to an Army fact sheet.

Some of the missiles in the system are designed to deliver a single, 500-pound warhead on a target through the use of satellite guidance, while others distribute hundreds of smaller bomblets over a larger distance, according to the Army.

North Korea’s apparent accomplishment puts it well ahead of schedule in its years-long quest to develop a true ICBM. The Hwasong-14 tested Monday could not have reached the U.S. mainland, analysts say, and there’s no evidence to date that North Korea is capable of building a miniaturized nuclear warhead to fit on one of its longer-range missiles. But there is now little reason to doubt that both are within North Korea’s grasp, weapons experts say.

Dana White, a Pentagon spokesperson, confirmed in a statement Tuesday night that the missile North Korea used was an intercontinental ballistic, and described it as a “escalatory launch.”

“The launch continues to demonstrate that North Korea poses a threat to the United States and our allies,” White said. “Together with the Republic of Korea, we conducted a combined exercise to show our precision fire capability.”

White said that the United States remains prepared to defend itself and allies and to use “the full range of capabilities at our disposal against the growing threat from North Korea.” The United States seeks only the peaceful denuclearization of the Korean Peninsula, and its commitment to its allies is ironclad, she added.

Washington Post writer Joby Warrick contributed to this report.