North Korea said Saturday it had offered to "temporarily" suspend any future nuclear test if the United States cancels its annual joint military drills with South Korea this year.

The government proposal was passed to the U.S. side through a "relevant channel" on Friday, the North's official KCNA news agency said.

Recent satellite images offer fresh evidence of North Korea developing a marine-based missile system that would give the nuclear-armed state a survivable second-strike nuclear capability, a U.S. think-tank said Friday.

The commercial satellite pictures suggest the conning tower of a new North Korean submarine -- first seen in July last year -- houses one or two vertical launch tubes for either ballistic or cruise missiles, the U.S.-Korea Institute at Johns Hopkins University said.

North Korea's top military body issued fresh warnings Thursday to the United States and South Korea over their "hostile" policies towards Pyongyang, as Seoul conducted a series of naval live-fire drills.

The National Defence Commission (NDC) criticised U.S. sanctions imposed after the North's alleged cyber attack on Sony Pictures and said Pyongyang would respond forcefully to continued provocation.

A North Korean soldier was shot dead by Chinese police after crossing the border and reportedly killing four people, Beijing acknowledged amid harsh criticism over slowness in releasing information.

"After the incident occurred, the Chinese police immediately launched a manhunt operation," foreign ministry spokesman Hong Lei said in comments posted on the ministry's website after a regular press conference on Wednesday.

Hundreds in Washington, New York and Canada rallied Wednesday night in the frigid cold proclaiming "I am Charlie" in solidarity with those killed in a deadly attack on French magazine Charlie Hebdo.

Some 200 to 300 French and American protesters gathered in the nation's capital in front of the Newseum, a museum dedicated to news, waving signs and French flags emblazoned with the now ubiquitous rallying cry "Je suis Charlie."

North Korea on Wednesday slammed the South after activists sent anti-Pyongyang leaflets over the border in balloons, warning that such launches have scuppered high-level talks in the past.

The isolated nation cautioned Seoul that the "reckless act" of leaflet scattering by North Korean defectors -- who it called "human scum" -- could threaten the tentative dialogue, state-run Korean Central News Agency (KCNA) said.

South Korea's defense ministry said Tuesday that North Korea appeared to have achieved a "significant" level of technology to miniaturize a nuclear device to be fitted on the tip of a missile.

The ministry made the warning in a white paper due to be released later Tuesday, although defense officials said the nuclear-armed North has yet to demonstrate its miniaturization capacity.

A North Korean believed to be a runaway soldier killed four Chinese citizens during a robbery after he crossed the border into China in search of food, media reports said Monday.

The young North Korean soldier crossed the border in late December and stole money and food at a house before killing four residents in China's northeastern city of Helong, South Korea's Yonhap news agency and Dong-A Ilbo newspaper said.

North Korea on Sunday lashed out at fresh sanctions imposed by the United States in retaliation for its alleged cyber attack on Sony Pictures, criticizing Washington for refusing a proposed joint investigation.

U.S. President Barack Obama last week authorized a new layer of sanctions on several Pyongyang institutions and officials, in the wake of the crippling hacking attack on the Hollywood movie studio. 

The United States imposed financial sanctions Friday on North Korea and several senior government officials in retaliation for a cyber attack on Hollywood studio Sony Pictures.

President Barack Obama said he ordered the sanctions because of "the provocative, destabilizing, and repressive actions and policies of the Government of North Korea, including its destructive, coercive cyber-related actions during November and December 2014."