North Korea on Friday accused the United States and South Korea of carrying out a "persistent and intensive" cyber attack against its official websites in recent days.

A number of official North Korean websites, including those of the Korean Central News Agency (KCNA), the daily Rodong Sinmun newspaper, and Air Koryo airline became inaccessible early Wednesday.

China's new President Xi Jinping and U.S. President Barack Obama held telephone talks Thursday on the expansion of ties, cyber-security and the situation in North Korea, state media reported.

Obama congratulated Xi on his new appointment after he was named president by China's parliament and said U.S.-China relations faced an historic opportunity for future cooperation, the Xinhua news agency said.

North Korean leader Kim Jong-Un has overseen a live-fire artillery drill near the disputed sea border with South Korea, state media said Thursday as the South's prime minister visited the flashpoint area.

The Yellow Sea border has witnessed bloody North-South clashes in the past and, with military tensions at their highest level for years, is seen as the prime location for another confrontation.

North Korea confirmed Wednesday that it had shredded the 60-year-old armistice ending the Korean War, and warned that the next step was an act of "merciless" military retaliation against its enemies.

A lengthy statement by the North's armed forces ministry added to the tide of dire threats flowing from Pyongyang in recent days that have raised military tensions on the Korean peninsula to their highest level for years.

North Korea leader Kim Jong-Un threatened to "wipe out" a South Korean island as Pyongyang came under new economic and diplomatic fire Tuesday from U.S. sanctions and U.N. charges of gross rights abuses.

Military tensions on the Korean peninsula have risen to their highest level for years, with the communist state under the youthful Kim threatening nuclear war in response to U.N. sanctions imposed after its third atomic test last month.

The United States on Monday slapped sanctions on North Korea's primary foreign exchange bank, as it bids to force the isolated nation to abandon its nuclear program.

The Treasury Department will impose sanctions on the Foreign Trade Bank (FTB) of North Korea after Pyongyang flouted international resolutions and conducted its third nuclear test last month, U.S. national security adviser Tom Donilon said.

Sanctions against North Korea over its nuclear program are not "the fundamental way" to resolve the crisis, China's foreign minister said Saturday, days after the U.N. tightened measures against Pyongyang.

China is the North's sole major ally and by far its biggest trading partner, including being its primary energy supplier.

China called for "calm and restraint" Friday after North Korea responded to new U.N. sanctions with fresh threats of nuclear war and promises to scrap peace agreements.

"China calls on relevant parties to exercise calm and restraint, and avoid actions that might further escalate tensions," foreign ministry spokeswoman Hua Chunying told reporters in Beijing.

With tensions surging on the Korean peninsula, North Korean leader Kim Jong-Un talked of "all-out war" as he toured a frontline unit that shelled the South in 2010, state media said Friday.

Visiting two islands close to the disputed maritime border with South Korea on Thursday, Kim said the North's military was "fully ready to fight a Korean style all-out war," the Korean Central News Agency (KCNA) said.

North Korea responded to new U.N. sanctions Friday with fresh threats of nuclear war, the scrapping of peace pacts with South Korea and the severing of a hotline with Seoul.

The latest measures announced by Pyongyang ramped up tensions on the Korean peninsula that have surged since the North staged a third nuclear test last month.