North Korea said Friday it had no choice but to "completely review" the nuclear issue after accusing the United States and South Korea over a plot to blow up a statue of its founding leader.

"Various circumstances compel us to completely review the nuclear issue," the North's foreign ministry said in a statement released through the official Korean Central News Agency (KCNA).

North Korean leader Kim Jong Un has been granted the title of marshal, state media reported Wednesday, cementing his status as the authoritarian nation's top military official as he makes key changes to the million-man force.

The decision to award Kim, who already serves as supreme commander of the Korean People's Army, was made Tuesday by the nation's top military, government and political officials, state media said in a special bulletin.

North Korea has named a new army vice marshal, state media said Tuesday, as part of a reshuffle apparently aimed at tightening young leader Kim Jong-Un's grip on the communist state's powerful military.

Hyon Yong-Chol, a veteran field commander, is now one of four people in the North to hold the rank of vice marshal of the Korean People's Army, and analysts say he is likely to become head of the 1.2-million-strong military.

North Korea's army chief has been relieved of all his posts due to illness, state media said Monday, in a surprise development that removes one of new leader Kim Jong-Un's inner circle.

Ri Yong-Ho is regarded as one of the key figures who has helped support the young, untested leader in the transition following the death in December of his father Kim Jong-Il, the longtime dictator of the reclusive state.

North Korea told Cambodia Saturday it was ready to rejoin six-party denuclearization talks, Phnom Penh said, without outlining any conditions to a potential return to the negotiating table.

North Korean Foreign Minister Pak Ui-Chun met with his Cambodian counterpart in Phnom Penh and "clearly stated that the Democratic People's Republic of Korea is ready to participate in the six-party talks", Cambodian foreign ministry spokesman Koy Kuong told reporters.

China has released four South Korean activists who were held in March after interviewing North Korean refugees hiding there, a report said Wednesday.

The four are being questioned by South Korean intelligence officials in China after being released from a detention center in the border city of Dandong just across from North Korea, Yonhap news agency said.

The United Nations agreed Tuesday to mediate between South and North Korea with the aim of forming a unified team for some events at the 2015 World University Games, organizers said.

Wilfried Lemke, the special U.N. adviser on sports for development and peace, signed a cooperation agreement with the Universiade organizing committee in the southwestern city of Gwangju.

The late North Korean leader Kim Jong-Il ordered his scientists to produce "a massive amount" of uranium bombs, according to internal regime documents, reports in Japan said Monday.

The instruction was revealed in papers believed to have been compiled in February this year for senior officials of the ruling Workers' Party, the Mainichi Shimbun and Tokyo Shimbun said.

The Russian government is this month set to agree a framework to settle North Korea's $11 billion debt to Moscow dating back to Soviet times, a deputy minister said.

Russia's Deputy Finance Minister Sergei Storchak made a rare visit by a top Russian official to Pyongyang from May 31 to June 2 to discuss the settling of the outstanding debt.

South Korea and the United States on Saturday launched a massive naval exercise in the tense Yellow Sea, ahead of the 62nd anniversary Monday of the outbreak of the Korean War, a spokesman said.

The three-day drill will involve 10 South Korean warships plus the USS George Washington aircraft carrier, 8,000 personnel and hundreds of combat aircraft, the Defense Ministry said.