More than a week after a South Korean ferry carrying 476 people capsized and sank, North Korea finally voiced its condolences Wednesday for the victims of the disaster, including the many schoolchildren who died.

The message was sent between the two Koreas' Red Cross organizations who regularly handle official cross-border communications, the South's Unification Ministry said.

South Korean President Park Geun-Hye on Wednesday urged Chinese leader Xi Jinping to make "further efforts" to dissuade North Korea from conducting a fresh nuclear test, warning of serious repercussions for regional stability.

Her comments, made during a phone call between the two presidents and reported by her office, came a day after South Korea said heightened activity at the North's main nuclear test site might indicate an imminent test.

The United States said Tuesday it was watching "very closely" following South Korean warnings that North Korea may be preparing a fourth nuclear test ahead of a visit to Seoul by President Barack Obama.

"North Korea has a history of taking provocative action and we are always mindful of the possibility that such an action could be taken," White House spokesman Jay Carney told reporters aboard Air Force One as Obama departed for his week-long trip to Asia.

North Korea could well be preparing to carry out a fourth nuclear test, South Korea said Tuesday, citing increased activity at its main test site just days ahead of a visit to Seoul by U.S. President Barack Obama.

"Our military is currently detecting a lot of activity in and around the Punggye-ri nuclear test site," defense ministry spokesman Kim Min-Seok told a press briefing.

The United Nations Security Council should slap targeted sanctions on North Korean officials responsible for grave human rights abuses, the head of a special U.N. inquiry said Thursday.

Michael Kirby told an informal meeting of the Security Council convened by Australia, France and the United States that he also wanted the reclusive regime hauled before the International Criminal Court (ICC) for prosecution.

Ugandan President Yoweri Museveni has thanked North Korea for providing military training, reports said Thursday, dismissing those who criticize a security deal which included training police and special forces.

"There are people who are not happy with them, but I have not seen any problem with them," Museveni said Wednesday, according to the Daily Monitor newspaper, speaking at the passing out parade of almost 700 police officers trained by the North Koreans.

North Korean leader Kim Jong-Un paid respects to his grandfather Kim Il-Sung as the country marked the birthday Tuesday of its late founder with renewed calls for loyalty to the ruling Kim dynasty.

At the stroke of midnight, Kim Jong-Un, accompanied by top military leaders, visited the Kumsusan Palace of the Sun in Pyongyang -- the mausoleum holding the embalmed body of his grandfather, the North's official KCNA news agency said.

North Korea on Monday warned South Korea it would pay a "dear price" for recent criticisms of Pyongyang's nuclear program and political system, saying they violated a no-slander agreement.

The warning from the Committee for the Peaceful Reunification of Korea (CPRK) came days after Pyongyang blasted South Korean President Park Geun-Hye's proposals for Korean reunification as the "daydreams of a psychopath".

Twelve countries seeking to abolish nuclear weapons on Saturday denounced North Korea's atomic program at the close of a meeting in Hiroshima, saying it endangered global stability.

The Non-Proliferation and Disarmament Initiative (NPDI) criticized North Korea for its nuclear and missile program and urged the reclusive state to accept inspections by the International Atomic Energy Agency (IAEA) and return to the Non-Proliferation of Nuclear Weapons (NPT).

North Korea on Friday accused the United States of hypocrisy for remaining silent over a South Korean missile test while condemning Pyongyang's recent launches.

"The U.S. double-dealing attitude and despicable mode of action has been brought to light," a spokesman for the North's powerful National Defence Commission (NDC) said in a statement.