SEOUL — Key North Korean websites suffered intermittent outages Tuesday after a nearly 10-hour shutdown that followed a US vow to respond to a crippling cyberattack on Sony Pictures, which Washington blames on Pyongyang.

It wasn’t immediately clear what caused the Internet stoppage in one of the least-wired and poorest countries in the world, but outside experts said it could be anything from a cyberattack to a simple power failure. The White House and the State Department declined to say whether the US government was responsible.

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Even if a cyberattack had caused the shutdown, analysts said, it would largely be symbolic since only a tiny number of North Koreans are allowed on the Internet — a fraction of Pyongyang’s staunchly loyal elite, as well as foreigners.

Though it denies responsibility for the Sony hack, North Korea’s government has called it a ‘‘righteous deed’’ and made clear its fury over Sony’s film ‘‘The Interview,’’ a comedy that depicts the assassination of the North’s authoritarian leader, Kim Jong Un, the head of a 1.2 million-man army and the focus of an intense cult of personality.

South Korean officials, speaking on condition of anonymity because of office rules, said the North’s official Korean Central News Agency and the Rodong Sinmun newspaper, which are the main channels for official North Korean news, had both gone down. But the websites were back up later Tuesday. Among the posts glorifying the ruling Kim family was one about Kim Jong Un visiting a catfish farm.

US computer experts described Monday’s Internet outages in the North as sweeping and progressively worse. Jim Cowie, chief scientist at Dyn Research, an Internet performance company, said in an online post that the North came back online after a 9½-hour outage. But the company said the North later suffered two outages, one lasting half an hour.

Possible causes for the shutdown include an external attack on its fragile network or even just power problems, Cowie wrote. But, he added, ‘‘We can only guess.’’

The outage was probably more inconvenient to foreigners, who can access the Internet through 3G networks, than to North Korean residents, most of whom have never gone online. There are only about 1,000 Internet Protocol addresses in North Korea for a population of 25 million, South Korean analysts say.

North Korea did not immediately release a response to the shutdown. But a commentary carried in state media Tuesday was filled with characteristic rhetoric, criticizing what it called a failed US policy on Pyongyang and comparing the United States to the Roman Empire, which, it said, ‘‘was thrown into a dumping ground of history as it collapsed while seeking prosperity through aggression and war.’’

Last year, North Korea suffered similar brief Internet shutdowns of websites at a time of nuclear tensions with the United States, South Korea, and other countries. North Korea blamed Seoul and Washington for the outages.

President Obama has said the US government expects to respond to the Sony hack, which he described as an expensive act of ‘‘cyber vandalism’’ by North Korea.

Obama did not discuss details, and it was not immediately clear whether the Internet connectivity problems represented the retribution. The US government regards its offensive cyber operations as highly classified.