By Ju-min Park

SEOUL (Reuters) - A North Korean missile appeared to have exploded just after it was launched on Wednesday, the U.S. and South Korean militaries said after detecting the latest in a series of weapons tests by the nuclear-armed state that have alarmed the region.

The launch attempt was made near the city of Wonsan, on North Korea's east coast, the same place it launched several intermediate-range missiles last year, all but one of which failed.

"U.S. Pacific Command detected what we assess was a failed North Korean missile launch attempt ... in the vicinity of Kalma," Commander Dave Benham, a spokesman for U.S. Pacific Command, said in a statement, referring to an air field in Wonsan.

"A missile appears to have exploded within seconds of launch," Benham said, adding that a more detailed assessment was underway.

A South Korean military official also said the missile appeared to have exploded just after it was launched.

It was not clear what type of missile it was. The South Korean defense ministry said it was conducting analysis to determine further details.

The increasing frequency of missile tests has fueled a growing sense of urgency over how to respond to isolated, unpredictable North Korea, which conducted its fifth nuclear bomb test in September.

It launched four ballistic missiles from near its west coast on March 6 and this week conducted a rocket engine test that its leader, Kim Jong Un, said opened "a new birth" of its rocket industry.

The latest launch came as the U.S. envoy for North Korea policy, Joseph Yun, met his South Korean counterpart in Seoul to discuss a response to the North's weapons programs.

Last week, U.S. Secretary of State Rex Tillerson visited Japan, South Korea and China and said that a policy of strategic patience with North Korea had ended, and all options, including a military one, were on the table if North Korea threatened South Korean or U.S. forces.

U.S. officials stress however that tougher sanctions will be the likely response for the time being, and a senior U.S. official told Reuters on Monday the Trump administration was considering these as part of a broad review of North Korea policy. North Korea is believed to be working to develop nuclear-tipped missiles that can reach the U.S. mainland, but experts believe it is still several years away from that capability.

John Wolfsthal, a senior director for non-proliferation and arms control at the U.S. National Security Council under former President Barack Obama, said it was difficult to pinpoint the cause of the missile test failures, but that North Korea's quality-control limitations were a likely factor.

"There are many, many things that have to go right for (a missile) to work," he said, adding that failures nevertheless provided North Korea with vital knowhow and experience that would eventually allow them to develop a working intercontinental ballistic missile.

"They will eventually learn ... and no amount of sanctions and isolation will slow them,” he said. “Eventually they will be able to make it work."

U.S. President Donald Trump rebuked Kim on Sunday, saying the North Korean leader was "acting very, very badly" and in a show of force in Tuesday, the U.S. Air Force said it deployed a B-1B Lancer strategic bomber in bilateral training missions in Japanese and South Korean airspace.

The United States is also deploying an advanced missile- defense system in South Korea, in spite of objections from China, North Korea's neighbor and only ally.

On Tuesday, a North Korean diplomat dismissed the threat of more sanctions and said his government would pursue an "acceleration" of its nuclear and missile programs, including a "pre-emptive first strike capability" and an inter-continental ballistic missile.

(Reporting by Idrees Ali, Jonathan Landay, Matt Spetalnick and David Brunnstrom in Washington, Kaori Kaneko and Chris Gallagher in Tokyo, Jiwon Choi and Christine Kim in Seoul; Writing by Robert Birsel; Editing by Simon Cameron-Moore and James Dalgleish)