Prime Minister Shinzo Abe lashed out at North Korea’s firing Wednesday of a medium-range ballistic missile into the Sea of Japan, just days ahead of a key summit between the U.S. and Chinese leaders expected to focus on reining in Pyongyang’s weapons programs.

The U.S. Pacific Command said it detected the launch at 6:42 a.m. from a land-based facility near Sinpo, home to a North Korean submarine base.

“(The launch) is a grave provocative action from a security standpoint, clearly violates U.N. Security Council resolutions and simply cannot be tolerated,” Abe told reporters.

In a statement, Pacific Command said its initial assessments indicated the type of missile was a KN-15 medium-range ballistic missile. The KN-15 is also known as the Pukguksong-2, a land-based variant of the submarine-launched Pukguksong-1, or KN-11.

In Tokyo, Chief Cabinet Secretary Yoshihide Suga met reporters at the Prime Minister’s Office around 8 a.m., saying the missile flew only “tens of kilometers” and landed outside Japan’s exclusive economic zone.

Suga said Tokyo had immediately lodged a protest with the North, denouncing the launch as a clear violation of resolutions adopted at the United Nations Security Council banning Pyongyang from the test-firing of ballistic missiles.

“Our country … won’t tolerate repeated provocative actions by North Korea,” Suga said. “We have filed a grave protest against North Korea and strongly denounced” the test-firing.

South Korea’s Defense Ministry also confirmed the test, saying the missile flew about 60 km, while the country’s Joint Chiefs of Staff said separately that the maximum altitude of its flight was 189 km.

The launch came a day after U.S. President Donald Trump threatened that the United States was ready to go it alone in reining in the recalcitrant North if China did not step in. The North’s nuclear arms and missile programs are likely to top the agenda at the first meeting of Trump and Chinese President Xi Jinping, which is scheduled for Thursday and Friday in Florida.

Abe said Japan would work closely with the United States and South Korea “to protect the lives and property of the public in any situation” as there is “a sufficient possibility” of North Korea taking more aggressive actions in the near future.

“North Korea is widely expected to be a major subject of the Xi-Trump summit,” said Robert E. Kelly, a professor of international relations at Pusan National University in South Korea. “Presumably, these sorts of launches signal to all parties that North Korea is not a pushover, not a pawn to be manipulated, but a tough actor in itself which will not simply passively agree to any deal made over its head.”

Wednesday’s launch was the latest in a spate of tests this year, including the near-simultaneous firing of four ballistic missiles into the Sea of Japan last month — a move the North said was a rehearsal for attacking U.S. bases in Japan. Those missiles, three of which fell into Japan’s exclusive economic zone, flew about 1,000 km. Abe characterized that test as “a new level of threat.”

Missile experts said the hypothetical target of that drill appeared to be U.S. Marine Corps Air Station Iwakuni in Yamaguchi Prefecture. Observers said the undisguised threat to U.S. bases in Japan was rare, even for Pyongyang, which routinely serves up colorful invectives.

In February, it also tested a Pukguksong-2, which uses solid fuel, from a mobile launcher. That launch, the first test of the missile, saw it fly about 500 km into the Sea of Japan.

Solid-fueled missiles involve a much smaller fleet of support vehicles than liquid-fueled missiles and can be prepared for launch much more quickly. They are also mobile, making them much more difficult to hunt down.

In addition to quicker launches, solid-fuel engines boost the power of ballistic missiles, giving them greater range.

Experts have said such missiles could supplement or replace the liquid-fueled Scuds and Rodongs that target South Korea and Japan.

North Korea said in February that the missile added “another powerful nuclear attack means … to the tremendous might of the country.”

“The advantage of the solid-fueled land variant of the SLBM is that it can be launched at very short notice,” said Euan Graham, director of the International Security Program at the Lowy Institute in Sydney. “That makes for a more survivable, battlefield missile. And also serves as a snap demonstration of capability recently called into question.”

On March 22, the U.S. said the North conducted a test-firing that appeared to fail “within seconds of launch.”

In addition, a top U.S. naval commander said Tuesday that the North appears to still be years away from fully mastering the technology needed to successfully deploy submarine-launched ballistic missiles (SLBMs).

“To launch those missiles from under the water is very, very complicated,” Pacific Fleet commander Adm. Scott Swift told South Korea’s Yonhap news agency. “I think it’s still years away before that technology is developed.”

He cited what the U.S. military has “seen and knows” but would not specify the grounds for his assessment, the report said.

Graham said the North’s ever-improving SLBM program has throttled expectations.

“Swift’s point about the complexity of underwater launches is well taken,” Graham said. “Frankly, I’m amazed that North Korea has developed the wherewithal to launch any kind of ballistic missile from a submarine.

“This is the nuclear big league they are playing in and it displays almost unbelievable ambition … that a country of North Korea’s limited resources would invest in a sea-based deterrent,” he added.

Graham said the break-neck speed with which it has been making progress in its SLBM effort — a program that would give it a potent “second-strike” deterrent from being attacked — “raises serious questions about the level of outside technical assistance they may have received.”

Pyongyang has conducted more than 20 missile launches and two nuclear tests over the past year as it seeks to master the technology needed to mount a warhead on a long-range ballistic missile capable of striking the continental United States. It has also been making apparent preparations for its sixth atomic test, according to analyses of recent commercial satellite imagery.

There has been growing speculation that Pyongyang will conduct an intercontinental ballistic missile test after leader Kim Jong Un used a New Year’s Day address to claim that the North was in the final stages of developing such a weapon.

Analysts say the North might time any nuclear and long-range rocket tests to the April 15 birthday of North Korea’s founder, Kim Il Sung, the late grandfather of the current leader.

Any nuclear or ICBM test would pose a fresh challenge to Trump, who has vowed that Pyongyang’s goal of possessing a nuclear-tipped long-range missile “won’t happen.”

Tillerson said this month during a visit to Asia that years of efforts to get the North to give up its nuclear weapons program have failed. Tillerson promised “a new approach,” saying that military action against the North “was on the table.”

But political messaging aside, Graham said Wednesday’s test-firing represented continued headway toward a more complete atomic deterrent.

“Kim Jong Un’s middle-finger message is very obviously directed at Trump and Xi,” Graham said.

“But we get so caught up on the political interpretation of these tests, let’s not forget the key point here is North Koreans are back in breakneck development mode, which suggest we perhaps ought to take (high-level North Korean defector) Thae Yong Ho’s warning about a fully fledged deterrent in 2017 more seriously.”

Staff writer Reiji Yoshida contributed to this report.