North Korea appears to have made some progress in developing its intermediate-range Musudan missile after a series of embarrassing failures earlier this year, the Defense Ministry said after Pyongyang tested-fired two of the missiles Wednesday.

The Defense Ministry said the North fired the first Musudan — which could reach as far as Guam — from the eastern coastal city of Wonsan at around 5:57 a.m. That missile burst into pieces and fell into the sea.

South Korea's Joint Chief Staff said that launch was assumed to be a failure, and Japanese Defense Minister Gen Nakatani also hinted that it was unsuccessful, saying "there seems to have been fundamental technical problems with the missile and its engine."

But about two hours after the first launch, at 8:03 a.m., the North lobbed a second missile from the same area that reached an altitude of over 1,000 kilometers and flew approximately 400 kilometers before falling into the Sea of Japan.

Nakatani said Pyongyang had shown "some capability" with the midrange missile, which has a potential range of 2,500 to 4,000 kilometers, and could target not only Japan, but much of Asia and the Pacific, including U.S. military bases in the region.

"This achievement means that the North now has more missiles that can reach Japan," Nakatani said. "The impact of the matter poses a grave concern to Japan's national security."

In an email to The Japan Times, U.S. Navy Cmdr. Dave Benham, a spokesman from the military's Pacific Command, said: "The missiles were tracked over the Sea of Japan, where initial indications are they fell." He added that NORAD (North American Aerospace Defense Command) had determined the launches did not pose a threat to North America.

Until Wednesday, North Korea had conducted four test-firings of what appeared to be Musudans since mid-April — all ending in apparent failures.

Japan was quick to react to the latest salvo.

In Oita Prefecture, where he was campaigning for next month's Upper House election, Prime Minister Shinzo Abe denounced the most recent provocation, telling reporters that the act "simply cannot be tolerated."

Deputy Chief Cabinet Secretary Koichi Hagiuda said that Japan had lodged a stern protest with Pyongyang via its embassy in Beijing.

The U.S., which led the charge to impose some of the harshest sanctions yet at the United Nations in March, also blasted the launch.

"These provocations only serve to increase the international community's resolve to counter (North Korea's) prohibited activities, including through implementing existing U.N. Security Council sanctions," State Department spokesman John Kirby said in a statement Wednesday.

Japan had been on alert for a launch after Nakatani ordered the Self-Defense Forces on Tuesday to prepare to intercept any ballistic missiles that flew near Japanese territory and waters.

The launch came just three days before the 66th anniversary of the eruption of the Korean War. The Korean Peninsula remains in a technical state of war because the 1950-53 conflict ended with an armistice, not a peace treaty.

Nakatani said Pyongyang could further intensify its saber-rattling, and that Tokyo was bracing for any further provocations.

Tuesday's launch underscores that Pyongyang is resolved to continue pursuing its nuclear ambitions despite the U.N. sanctions, which explicitly ban the hermit nation's use of ballistic-missile technology.

At the North Korean Worker's Party Congress in May, supreme leader Kim Jong Un was defiant, lauding his country's successful nuclear test in January and satellite launch in February.

Kim has been calling on the U.S. to start peace talks, but Washington argues that Pyongyang should first denuclearize before any conversation begins.

Meanwhile on Wednesday, senior diplomats and experts from all countries involved in the six-party North Korean denuclearization talks attend a two-day security forum in Beijing.

Representatives from North Korea — participating in this year's North Asia Cooperation Dialogue for the first time since 2012 — joined officials from Japan, the U.S., South Korea, China, and Russia. Media reports said that the U.S. and South Korean delegations criticized North Korea at the meeting.