(CNN) -- North Korea's state media released a "detailed report" Tuesday claiming that American journalists Laura Ling and Euna Lee entered the country illegally in order to record material for a "smear campaign" against the reclusive communist state.
Supporters rally for U.S. journalists Euna Lee and Laura Ling on June 4 in Seoul, South Korea.
It added that the two women "admitted that what they did were criminal acts ... prompted by the political motive to isolate and stifle the socialist system of the DPRK by faking up moving images aimed at falsifying its human rights performance and hurling slanders and calumnies at it."
Ling and Lee were sentenced this month to 12 years of hard labor in North Korea.
They were arrested in March for "having illegally trespassed into the border of the DPRK [Democratic People's Republic of Korea, as North Korea is officially known] and committed hostile acts against it for which they were tried."
South Korean President Lee Myung-bak urged North Korea to release the two journalists Tuesday in a joint appearance with U.S. President Barack Obama at the White House. Obama did not mention them. Relations between North and South Korea are extremely tense. Watch family members plead for women »
The reporters for California-based Current TV -- a media venture of former U.S. Vice President Al Gore -- were arrested while reporting on the border between North Korea and China. They were sentenced after a closed-door trial.
"The investigation proved that the intruders crossed the border and committed the crime for the purpose of making animation files to be used for an anti-DPRK smear campaign over its human rights issue," the Korean Central News Agency said Tuesday.
The KCNA report said there were two unidentified men with Ling and Lee when they were arrested, but gave no further details. It did not say whether the men were arrested.
In a joint statement June 8, the journalists' families said they were "shocked and devastated" by the trial and sentence and urged Pyongyang "to show compassion and grant Laura and Euna clemency and allow them to return home to their families."
"Laura and Euna are journalists who went to the China-North Korea border to do a job," they said. "We don't know what really happened on March 17, but if they wandered across the border without permission, we apologize on their behalf and we are certain that they have also apologized."
The KCNA report Tuesday said they had "covertly crossed the River Tuman" into North Korea.
In Washington, Secretary of State Hillary Clinton told reporters earlier this month the United States is seeking the immediate release of the two journalists on humanitarian grounds.
"Obviously, we are deeply concerned about the length of the sentences and the fact that this trial was conducted totally in secret with no observers," she said June 8. "And we are engaged in all possible ways, through every possible channel, to secure their release."
The families said Ling suffers from an unspecified "serious medical condition" and Lee has a 4-year-old daughter "who is displaying signs of anguish over the absence of her mother."
"We believe that the three months they have already spent under arrest with little communication with their families is long enough," they said.
The United States has no diplomatic relations with North Korea, and Sweden represents U.S. interests there. The Swedish ambassador told the U.S. State Department that no observers were allowed in the courtroom for the trial, and the ambassador was allowed to see Lee and Ling only three times.
CNN's Suzanne Malveaux in Washington contributed to this report.