A North Korean missile launch likely failed on Tuesday, the U.S. and South Korean militaries said, the fourth in a series of high-profile failures that somewhat tempers recent worries that the North is pushing quickly toward its goal of a nuclear-tipped missile that can reach America's mainland.

South Korea's Yonhap news agency said the missile was a powerful intermediate-range Musudan, which could potentially reach U.S. military bases in Asia and the Pacific.

Yonhap cited an unidentified government source as saying the missile exploded at a mobile launch pad as soon as the launch button was pressed. The report, if confirmed, suggests the missile may have even failed to lift off. Yonhap did not say how its source obtained the information.

South Korea's military couldn't confirm the report. The Joint Chiefs of Staff said in a statement that North Korea attempted to launch an unidentified missile early in the morning from the eastern coastal town of Wonsan, but that it likely failed. It released no other details.

The U.S. Department of Defense said in a statement that its assessment also indicated that the launch was a failure. It condemned the launch as a violation of U.N. Security Council resolutions that prohibit North Korea from using ballistic missile technology.

Despite the recent failures, there have been growing worries about North Korea's nuclear and missile activities this year, which include a nuclear test in January and a rocket launch in February that outsiders saw as a test of banned long-range missile technology.

White House spokesman Josh Earnest said the failed missile test did not pose a threat to North America. But he cautioned that "North Korea's continued pursuit of ballistic missile and nuclear weapons capabilities pose a significant threat to the United States, our allies, and to the stability of the greater Asia-Pacific."

North Korean leader Kim Jong Un issued an order in March that tests be conducted of a nuclear warhead and ballistic missiles capable of carrying such warheads. The order was thought to be part of North Korea's response to annual South Korea-U.S. military drills that it sees as a rehearsal for an invasion.

"I think they keep firing (Musudans) because they've continuously failed" in previous launches, said Lim Eul Chul, a North Korea expert at South Korea's Kyungnam University. "They'll continue to make efforts to upgrade (Musudan's) capability to a level that can satisfy their leader."

South Korea has dismissed as "propaganda" repeated overtures by North Korea for talks, which some analysts see as an attempt by the North to win concessions from its rivals. South Korea's Foreign Ministry warned Tuesday that North Korea will face stronger sanctions if it doesn't stop provocations.

Lim said Tuesday's launch attempt shows that North Korea is openly pressing ahead with its vow to bolster its military strength, regardless of whether it is pushing for talks with South Korea. "For them, upgrading Musudan's capability is a different matter from seeking a dialogue with South Korea," he said.

In April, North Korea attempted unsuccessfully to launch three suspected Musudan missiles. All exploded in midair or crashed, according to South Korean defense officials.

Musudan missiles are thought to have a potential range of about 3,500 kilometers (2,180 miles), which would put U.S. military bases in Guam within their striking distance. South Korea believes North Korea does not have a functional long-range missile capable of hitting the U.S. mainland, but that the North is working on that technology.

Before April's suspected launches, North Korea had never flight-tested a Musudan missile, although one was displayed during a military parade in 2010 in Pyongyang, its capital.

Daniel Russel, the top U.S. diplomat for East Asia, said Tuesday that high-level talks between the U.S. and China in Beijing next week would provide an opportunity to "game out" how to pressure North Korea to agree to negotiations on the denuclearization of the Korean Peninsula.

"That's not unconditional surrender. That's a reasonable and consistent objective of ours. We have a vastly improved chance of getting that with China's full cooperation," Russel told reporters in Washington.

In March, Beijing signed up to the toughest U.N. sanctions yet against North Korea. China is a traditional ally of the North and its main trading partner but relations have been strained over Pyongyang's development of nuclear weapons and ballistic missiles.