A former US government contractor pleaded guilty Friday to leaking "highly classified intelligence" about North Korea's nuclear program and will serve 13 months in prison, officials said.

Stephen Jin-Woo Kim, a former Lawrence Livermore National Laboratory employee who was assigned to the State Department, agreed to the plea, which must be approved by a judge, according to the US Justice Department.

Kim was charged with leaking information to Fox News reporter James Rosen in a case that sparked concern about a war on news media, because Rosen was named as a "co-conspirator" in the case.

The leak revealed the US assessment of military capabilities and preparedness of North Korea. It became the subject of a Fox News dispatch within hours of the 2009 release.

"Today Stephen Kim admitted to violating his oath to protect our country by disclosing highly classified intelligence about North Korea's military capabilities," said US Attorney Ronald Machen in a statement.

"Stephen Kim admits that he wasn't a whistleblower. He admits that his actions could put America at risk," Machen added.

Kim is to be sentenced on April 2 by District Court Judge Colleen Kollar-Kotelly on one count of making an unauthorized disclosure of national defense information. Under the agreement, he would get one year of supervised release after his prison term.

Defense attorney Abbe Lowell said in a statement that Kim "did what so many government officials do every day in Washington, DC: he talked to a reporter.

"Regrettably, the topic and some of the information that he discussed with a reporter was also contained in a classified report."

The attorney said Kim was a victim of "over-classification" of information by the government, adding that "a great deal of harmless information is 'classified,' even when it is widely available to the public."

"Faced with the draconian penalties of the Espionage Act, the tremendous resources that the federal government devoted to his case," which included a half-dozen prosecutors and a dozen FBI agents, "and the prospect of a lengthy trial in today's highly-charged climate of mass disclosures, Stephen decided to take responsibility for his actions and move forward with his life," the lawyer said.

Trevor Timm at the Freedom of the Press Foundation said the case highlighted an unfair use of the Espionage Act to crack down on news leaks.

By using the law, Timm said, "it doesn't matter if the information leaked by Kim was properly classified, or if it should have been classified at all. Kim could not argue the information he gave to Rosen may have been innocuous."

"The ruling also gives the government carte blanche power to classify whatever it wants -- including waste, abuse, and crimes -- and keep it secret under the threat of prosecution of anyone who could potentially reveal it," Timm said in a blog post Friday.

S. Korea president tells North to stick to reunion plan
Seoul (AFP) Feb 07, 2014 - South Korean President Park Geun-Hye on Friday warned North Korea not to renege on its agreement to host a reunion for families divided by the Korean War.

Park's comments came a day after Pyongyang said it would have to reconsider its commitment to the reunion event, citing South Korean-US military exercises and "slanderous" articles in the South Korean media.

The two rivals had agreed during rare talks on Wednesday, to hold the reunion for several hundred separated relatives from February 20-25.

A similar event had been planned last September, but North Korea cancelled at the last minute -- an act that President Park stressed should not be repeated this time around.

"North Korea must not hurt the separated families so deeply again", a press pool report quoted Park as saying before the start of a security meeting with government and military officials.

Park said the reunion would provide momentum for reconciliation on the Korean peninsula, but voiced concern over "instability" in Pyongyang following the recent purge and execution of North Korea leader Kim Jong-Un's uncle and political mentor Jang Song-Thaek.

Despite the doubt now hanging over the reunion, more than 60 South Korean officials crossed into the North on Friday to inspect the Mount Kumgang resort venue where it is to be held.

"We are going to strive to fully prepare for the events by checking and repairing facilities so the elderly can conveniently meet their loved ones," Park Geuk, a South Korea Red Cross official, was quoted as saying by Yonhap news agency.

Among the delegation were officials from the South's giant Hyundai corporation, which constructed the Kumgang resort as a destination for South Korean tourists.

The facility was opened in 1998, but the tours were suspended in 2010 after North Korean guards shot dead a female tourist who had wandered off the approved path.

North Korea has played both hawk and dove with the South since the start of the year, threatening Seoul if it pushes ahead with the US joint exercises, while also proposing a series of potential tension-reducing measures.

"Recently, North Korea has launched an apparent peace offensive but we must keep our guard up all the more," Park said.

"We must maintain a firm defence posture in order to prevent provocative acts by the North and if it provokes us, we have to punish them thoroughly", she added.

Millions of Koreans were separated by the 1950-53 Korean War, and the vast majority have since died without having any communication at all with surviving relatives.