The White House called Monday on North Korea to stop seeking to exploit its detention of an American man for political and diplomatic gains.

Pyongyang announced last year that it "would not use the fate of Kenneth Bae as a political bargaining chip," White House Press Secretary Jay Carney told reporters here.

His comments came after North Korea again canceled its invitation for Amb. Robert King, special envoy for North Korean human rights issues, to visit Pyongyang for talks on the Bae issue.

Bae, a 45-year-old Christian missionary, has been detained there for 15 months.

Carney reiterated Washington's deep disappointment over the communist regime's decision.

He added the U.S. will continue to work actively to secure Bae's release.

King reportedly had planned to travel to North Korea this month. It's the second time that the secretive communist country abruptly reversed its decision to allow his trip.

The exact reason for the North's move this time remains unconfirmed. But many speculate it relates to Pyongyang's traditional displeasure with South Korea-U.S. military exercises, the next round scheduled for later this month.

"We remind the DPRK (North Korea) that the U.S.-ROK (South Korea) military exercises are transparent, regularly scheduled and defense-oriented," Carney added. "These exercises are in no way linked to Mr. Bae's case, and we believe they know that."

Bae's family openly expressed hope that the Rev. Jesse Jackson, who twice sought the U.S. presidency, would take up the captive's cause. He secured the freedom of a U.S. Navy pilot held by Syria in 1983 after meeting with the late Syrian president Hafez al-Assad, father of the current president, in Damascus.

In a separate press briefing, the State Department said the U.S. is doing everything it can to resolve the Bae issue.

"We've said repeatedly that this is a top priority for us, and we're going to pursue all avenues to have him released," Marie Harf, the State Department's deputy spokeswoman, said at a press briefing.

She said the U.S. government is not involved in the ongoing trip to Pyongyang by Donald Gregg, former U.S. ambassador to Seoul.

"It's a private delegation," Harf said.

The North's state news agency, KCNA, reported Monday (local time) that Gregg, now chairman of the U.S. Pacific Century Institute, and other members of the institute are in Pyongyang for unspecified reasons. (Yonhap News)