Chinese nuclear experts believe North Korea may already have a nuclear arsenal of 20 warheads and the uranium enrichment capacity to double that figure by next year, the Wall Street Journal reported Thursday.

The estimate, which the Journal said was relayed to U.S. nuclear specialists in a closed-door meeting in February, is significantly higher than any previously known Chinese assessment.

South Korea and the United States have agreed a new nuclear pact allowing Seoul to expand its civil atomic energy program, wrapping up more than four years of negotiations, a report said Wednesday.

A signing ceremony will be held at 4:15 pm (0715 GMT) in Seoul, a South Korean foreign ministry official said without revealing contents of the deal.

North Korean leader Kim Jong-Un has scaled the country's highest mountain, state-run media said Sunday, arriving at the summit to tell troops that the hike provides mental energy more powerful than nuclear weapons.

A photo of the leader of the isolated state showed a smiling and wind-swept Kim standing on a snow-covered mountaintop, the sun rising behind him.

North Korea celebrated the birth anniversary Wednesday of founder Kim Il-Sung, with current leader Kim Jong-Un paying respects at his grandfather's mausoleum, as rights groups highlighted his "horrific" human rights legacy.

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's first lady has appeared in public for the first time this year as part of celebrations marking the birthday of the country's founding leader Kim Il-Sung, state media said Tuesday.

A grinning Ri Sol-Ju, wearing what appeared to be a wedding ring on her left hand, was pictured clapping next to her smiling husband Kim Jong-Un during a men's football match at Kim Il Sung Stadium on Monday, the North's Korean Central News Agency (KCNA) said.

Defense Secretary Ashton Carter promised Friday that the U.S. would deploy state of the art weaponry in Asia, including the latest stealth bombers and cyber warfare units, to counter threats posed by the likes of North Korea.

"Our newest and best things are being deployed to this part of the world," Carter said in Seoul -- the second leg of a visit to the two key U.S. military allies in the region, Japan and South Korea.

North Korea on Thursday vowed to continue its push to develop nuclear weapons as well as ease chronic food and energy shortages during a rare parliamentary session that was closely watched by observers.

The announcement made following the meeting -- one of the few opportunities to gauge the mood inside the reclusive nation -- stuck closely to a New Year's speech by leader Kim Jong-Un which stressed the need to improve people's living standards.

U.S. Defense Secretary Ashton Carter arrived in South Korea on Thursday for a visit dominated by the issue of North Korea, which fired off two missiles as the Pentagon chief flew to the region.

Carter arrived from Tokyo on the second leg of a trip to the two key U.S. military allies in Asia.

The United Nations on Wednesday launched an appeal for $111 million dollars to help 70 percent of North Korea's population now facing a food crisis.

The funding will help five U.N. agencies working on the ground to continue providing North Koreans with food, clean water and other basics in 2015.

North Korea test-fired four short-range missiles into the sea off its west coast Friday in an operation apparently supervised by leader Kim Jong-Un amid heightened military tensions, a South Korean military spokesman said.

The missiles were launched from a base on the west coast and flew more than 100 kilometers (60 miles), the spokesman for the South's joint chiefs of staff told AFP.