North Korea, usually blamed for hacking others, has accused the United States of staging cyber attacks against its Internet servers after reports of disruptions to its main news services, the latest twist from an increasingly bellicose North.
Russia's Itar-Tass news agency said a "powerful hacker attack" from abroad had brought down Internet servers inside the North, disabling access to some websites.
The accusation comes at a time of increased tension between reclusive North Korea and South Korea, along with the South's ally the United States.
The North has threatened a nuclear war with the United States in response to new United Nations sanctions over its latest nuclear test and to strike back at the South and the United States during military drills they are staging.
South Korea's MBC television said the North's state media services were among those affected by the cyber attack.
These included the websites of the KCNA news agency and the official Rodong Sinmun newspaper, which were said to be experiencing disruptions even though they were operating normally on Thursday and Friday.
"It is nobody's secret that the U.S. and the South Korean puppet regime are massively bolstering up cyber forces in a bid to intensify the subversive activities and sabotages against the DPRK," KCNA said on Friday.
"Intensive and persistent virus attacks are being made every day on Internet servers operated by the DPRK," it said.
The Democratic People's Republic of Korea, or DPRK, is the North's official name.
KCNA and Rodong Sinmun have carried the North's increasingly strident rhetoric of late, accusing the United States and South Korea of staging preparations for war and vowing to scrap the armistice that stopped fighting in the 1950-53 Korean War.
The North has also threatened to use nuclear weapons against what it called hostile forces.
North Korea in turn has been blamed for spreading malicious software that crashed the websites of government agencies and businesses, and for a cyber attack on a South Korean state-run bank server in 2011 that took more than a week to restore.
North Korea denies charges of cyber attacks and accuses the South of a conspiracy to fuel confrontation, although defectors from the North have warned that Pyongyang was recruiting thousands of computer engineers to its cyber warfare unit.
Military experts said cyber warfare was a major threat from North Korea, along with its conventional forces and its weapons of mass destruction programme, that posed a security risk to utilities and communications networks in the South.
North Korea also has been accused of jamming global positioning system signals affecting hundreds of flights at South Korea's main airport.
Earlier this week, U.S. spy agencies said for the first time that cyber attacks and cyber espionage had supplanted terrorism as the top security threat facing the United States.
The United States and China also are embroiled in a row over cyber warfare, with U.S. President Barack Obama calling his Chinese counterpart Xi Jinping to discuss the issue this week.