SEOUL, South Korea — North Korea, a country paranoid about perceived threats from the outside world, said Friday that it had found new foreign invaders: hackers from the United States and its allies shutting down the North’s websites, the country’s main tool of spreading propaganda abroad.

Until now, the complaint came from the other direction, with South Korean officials suspecting that North Korea was behind a recent series of hacking attacks on South Korean and U.S. websites. After North Korea’s recent threats to retaliate against U.N. sanctions, South Korea warned of possible North Korean efforts to disrupt the Internet in the South, one of the most wired countries in the world.

These accusations, although denied by the opposing sides, showed how inter-Korean tensions are increasingly spreading into cyberspace.

“It is nobody’s secret that the U.S. and South Korean puppet regime are massively bolstering up cyberforces in a bid to intensify the subversive activities and sabotages against the DPRK,” the North’s Korean Central News Agency said, using the acronym of the country’s official name, Democratic People’s Republic of Korea. “They are seriously mistaken if they think they can quell the DPRK’s voices of justice through such base acts.”

North Korea’s often strident rhetoric has escalated to a feverish new pitch in recent weeks, complete with a threat to launch a “pre-emptive nuclear attack” at the United States and South Korea after the allies started joint military drills on March 1, followed by new U.N. sanctions for the North’s Feb. 12 nuclear test.

North Korea did not elaborate on what it called “intensive and persistent virus attacks” on its Internet servers. But Russia’s Itar-Tass news agency said a “powerful hacker attack” from abroad had brought down Internet servers inside the North. Nevertheless, the North’s two main channels of government statements and propaganda — the websites of the Rodong Sinmun newspaper and the Korean Central News Agency — operated normally Friday.

In a report titled “Enemies of the Internet,” the group Reporters Without Borders included North Korea on a list of countries that “censor Internet access so effectively that they restrict their populations to local intranets that bear no resemblance to the World Wide Web.”