Citing unidentified sources in the South Korean government, Yonhap news agency said Clinton may head back to Washington less than a day after arriving in Pyongyang.
Washington, the sources said, has made it clear that its current diplomatic standoff with Pyongyang is a separate matter from the efforts to release the two journalists, sentenced to 12 years in prison for illegally entering the secretive nation earlier this year.
Clinton met with North Korean leader Kim Jong Il and conveyed a message from President Obama, the official Korean Central News Agency said in a report from Pyongyang.
White House Press Secretary Robert Gibbs said in a statement this morning: "While this solely private mission to secure the release of two Americans is on the ground, we will have no comment. We do not want to jeopardize the success of former President Clinton's mission."
Clinton, the husband of Secretary of State Hillary Rodham Clinton, is the highest-profile U.S. official to visit North Korea in nearly a decade. His surprise visit comes as Washington presses other nations to curb ties with the country, which recently resumed its nuclear program and tested ballistic missiles in defiance of United Nations resolutions.
In Washington, a person familiar with the mission said the negotiations leading to Clinton's trip "lasted for months."
He said that although North Korea's nuclear negotiator, Kim Kye Gwan, was among those who received Clinton at the airport, the former president's goals were strictly humanitarian, and he had no intention to delve into the disputed disarmament issues.
Among the officials deeply involved in the negotiations was Sen. John F. Kerry, (D-Mass.), chairman of the Senate Foreign Relations Committee.
Laura Ling and Euna Lee of San Francisco-based Current TV were taken into custody in March near the border with China while reporting on refugees fleeing North Korea. They were sentenced to hard labor for illegal entry and "hostile acts."
Lisa Ling, the sister of reporter Laura Ling, said Monday that the family could not comment on the report.
"Everything is just so delicate," she said. "We're going to wait it out a while longer. We're on pins and needles."
White House and State Department officials declined to comment on the mission, as did a spokeswoman for former Vice President Al Gore, a co-founder of Current TV. But another U.S. official, who declined to be identified, confirmed the mission. He said the Clintons were approached by the journalists' families when it became clear the North Koreans would permit a visit.
U.S. officials and North Korea watchers have predicted for some time that Pyongyang could be open to a visit from a high-ranking dignitary to discuss the women's imprisonment.
With its love of pomp and circumstance, North Korea in the past has used celebrity visits for propaganda, trying to show that the outside world validates its system of government.
Scott Snyder of the nonprofit Asia Foundation said Clinton's standing as a world statesman carried weight with Pyongyang.
"The North Koreans have a lot of nostalgia for the end of the Clinton administration," he said.
"The question is going to be how could he go to Pyongyang without some assurance that they would be released," Snyder said.
"For someone at his level to go without a prior assurance of some kind would be to risk a huge loss of face."