Former U.S. President Jimmy Carter may soon travel to North Korea as part of his efforts, not always fruitful, to broker the resumption of dialogue and win the release of a Korean-American man detained there, diplomatic sources said Wednesday.

But the South Korean and U.S. governments apparently take a dim view of Carter's possible trip to North Korea out of concern that the communist nation may try to exploit it for propaganda purposes.

Carter recently sent a letter to Secretary of State John Kerry, calling for talks with North Korea and expressing his intent to visit Pyongyang again, a source said, requesting anonymity.

"North Korea appears to have invited him to visit," the source said.

If Carter makes a trip to Pyongyang, he is expected to use it as a chance to request the release of Kenneth Bae, a tour operator held in the North for nearly half a year, according to another source.

Efforts to free him have taken further urgency following Pyongyang's announcement last week he would stand trial on unspecified charges of crimes against the state.

The State Department would not talk openly about Carter's possible visit to the North.

Carter doesn't need to give prior notice to the U.S. government or get permission from it for any trip to North Korea, a department official pointed.

"You need to speak to President Carter's office about any questions regarding his alleged travel," the official said on background.

An email inquiry to Carter's press secretary, Deanna Congilio, led to an automatic reply, "I am out of the office on leave."

Officials at the South Korean Embassy in Washington said they have not heard about the issue.

"We are not aware of anything (related to Carter's possible trip)," an embassy official said.

The official expressed doubt that Carter will bring Bae back home or produce any breakthrough in coaxing Pyongyang to return to the bargaining table.

"But we don't rule out the likelihood that former President Carter will visit North Korea as a private citizen since he is a member of The Elders," the official said.

The Elders is an independent group of about 10 former heads of state.

Carter last visited North Korea in April 2011 along with a few other members of The Elders. He failed to meet then-North Korean leader Kim Jong-il.

At that time, many South Koreans disapproved of the trip, which they regarded as having produced no tangible results. Carter's group was merely misused by the North Koreans for propaganda, critics claimed.

  In 2010, however, Carter won plaudits when he negotiated the release of American national Aijalon Mahli Gomes, sentenced to eight years of hard labor for illegally crossing into the North from China.

Carter, who served as U.S. president from 1977 to 1981, is known for his initiative to promote the peace on the Korean Peninsula and around the world. (Yonhap News)