(CNN) North Korea claimed on Thursday to have conducted a successful test-firing of a intermediate-range missile -- an apparent reference to a missile that the South Korean military said was fired into the sea one day earlier.

The military state's government-run news agency reported that the country fired a Hwasong-10 -- also known as a Musudan -- and that it landed accurately in waters about 400 kilometers (249 miles) down range.

The statement was reiterated by a North Korean Foreign Ministry official at its embassy in Beijing.

"We are very happy. The Hwasong-10 means our transportation method has clearly succeeded. This means we can now confidently deal with whatever nuclear war the U.S. forces," Choe Sonhui, the General of the Department of U.S. Affairs of North Korea Foreign Ministry said at a news conference.

"What we are doing is trying to cope with the current situation where the United States is trying to threaten the DPRK with nuclear weapons, so we are trying to strengthen our nuclear capabilities in order to cope with threats that are imposed on the DPRK," she added, using an acronym for the country typically used by government officials.

However, South Korean and U.S. officials previously said that North Korea had fired two Musudan intermediate-range missiles from its eastern coast on Wednesday morning, including one that traveled 400 kilometers before it fell into the Sea of Japan.

The other flew 150 kilometers (93 miles) and is considered a failed launch, according to a South Korean military official.

The South Korean military's assessment of North Korea is that it has "significantly improved their Musudan missile's engine technology," according to a statement from the spokesperson of the South Korean Joint Chiefs of Staff. The spokesperson added that it was too early to call the second North Korea launch Wednesday a success.

Cmdr. Dave Benham, spokesman for the U.S. Pacific Command, said this week that both missiles were believed to have fallen into the Sea of Japan, also known as the East Sea.

North Korea's latest test of the Musudan missile was a "partial success" which has "finally demonstrated the full performance of the missile's propulsion system," according to analysis from 38 North, a North Korea monitoring project based in Washington, DC.

The report says that although the Musudan is "not a reliable weapon," the launch "increases the likelihood" that North Korea's intercontinental ballistic missiles (ICBMs) "will reach operational status early in the next decade."

North Korea has previously made at least four previous attempts this year to test Musudan missiles.

The first missile launch on Wednesday took place at 5.58 a.m. local time, just two hours before the second missile was fired at 8.05 a.m..

Both were launched from the North Korean port city of Wonsan.

After the first test on Wednesday, Japanese Prime Minister Shinzo Abe had said that his country could "never forgive" the action, which he stressed was in violation of U.N. resolutions.

"We can never forgive this and lodged a firm protest," he told reporters from Kumamoto, southern Japan.

"We would like to continue taking a close coordination with the U.S. and South Korea and working on North Korea (at) the United Nations, so that North Korea would not conduct such an action again."

In a statement the U.S. State Department said they condemned the missile launches. "We are aware of reports that the DPRK fired two ballistic missiles. We are monitoring and continuing to assess the situation in close coordination with our regional allies and partners."

North Korea's Musudan obsession

The military state has taken an intense interest in the Musudan missile in 2016, an intermediate-range weapon with a strike range of 2,500 to 4,000 kilometers.

It conducted its fourth Musudan test in May , which exploded after only flying for about two or three seconds, according U.S. defense officials.

One month earlier, another twin missile test failed , while on the anniversary of North Korean founder Kim Il Sung's birthday in April, another Musudan missile was reportedly launched unsuccessfully

"(Kim Jong Un) is interested in being the leader of North Korea who has been able to create a deliverable nuclear weapon, and clearly they're counting on this intermediate range Musudan missile to do that," Christopher Hill, the former U.S. Ambassador to South Korea, told CNN.

"The key element of it is that it's mobile. The fixed launch points, we know precisely where they are, but if this thing pops out a forest we don't."

While the second missile launched by North Korea on Wednesday might not have reached its full range, aerospace engineer John Schilling said it might count as a partial success simply because it flew at all.

"It didn't blow up on the pad and it flew far enough that patient engineers might have learned something from it," he told CNN.

"But as they didn't stop to figure out what went wrong after today's first test, it is pretty clear that they aren't working patiently and trying to learn from their mistakes."

South Korean Defense Minister Han Minkoo told CNN's Paula Hancocks in the 18 years of Kim Jong Il's reign there were 18 missile tests by North Korea, compared to 27 launches in just four years under his son.

The ramp up in missile testing could be due to growing financial stresses in North Korea, as U.N. sanctions begin to create serious challenges for the country.

"North Korea is on the verge of feeling quite substantial economic distress," University of California San Diego Korea-Pacific program director Stephan Haggard said.

"Part of the effort here is to get attention focused back on North Korea, so that perhaps they think they can get some relief from the sanctions instituted recently."