WASHINGTON (AFP/REUTERS) - North Korea has freed one of three Americans detained in the isolated country, surprisingly allowing a Pentagon plane to land there on Tuesday before whisking him away.

The White House confirmed that American tourist Jeffrey Fowle, 56, had been released from North Korea, had departed the country and was on his way home to his family.

White House spokesman Josh Earnest said Fowle that the United States welcomed the move but remained focused on getting two other US citizens released as well.

"While this is a positive decision ... we remain focused on the continued detention of Kenneth Bae and Matthew Miller and again call on the DPRK to immediately release them," Earnest said, referring to North Korea.

US officials said Pyongyang had given Washington a timeframe within which to transport Fowle out of the country, and the Pentagon had decided to send in a plane to bring him home, even though Washington does not have diplomatic ties with communist North Korea.

US State Department deputy spokeswoman Marie Harf thanked Swedish diplomats for their efforts to secure his freedom.

Fowle had been checked by doctors and "appears to be in good health," Harf told reporters, adding the plane had flown from Pyongyang to Guam and he would head next to the mainland US.

She refused to go into specifics however about when he was expected to arrive home in the state of Ohio.

She would also not reveal how Fowle's release was brokered.

"I'm not going to confirm any details about the discussions or the ways we tried to get our American citizens home," Harf said.

Earlier this month, Fowle made a renewed plea for the US government to work to secure his release.

In an interview published by the pro-North Korean Japanese newspaper Chosun Sinbo, Fowle said he was extremely "anxious" that he would share the fate of his already tried and jailed fellow detainees.

Fowle entered the North in April and was detained after apparently leaving a Bible in the bathroom of a nightclub in the northern port of Chongjin.

His plea came only two weeks after Miller was sentenced to six years' hard labor by the North Korean Supreme Court.

The 24-year-old was also arrested in April after he allegedly ripped up his visa at immigration and demanded asylum.

The third detainee, 42-year-old Korean American Kenneth Bae, was arrested in November 2012 and later sentenced to 15 years' hard labour.

Harf said "the US government will continue to work actively on" the cases of Miller and Bae, and repeated US offers to send a State Department envoy, Robert King, to the isolated North to discuss their plight.

Washington has condemned Pyongyang over the detentions, saying the men were being held as political hostages to extract diplomatic concessions.

The North has repeatedly denied King a visa, apparently hoping a more high-profile envoy will be sent to the country.

The nuclear-armed North wants a resumption of stalled six-party nuclear negotiations, but the United States and South Korea insist it must first show a tangible commitment to denuclearization.