North Korea lost what little access it had to the Internet on Monday as outside connections to the small communist country went dark.
The digital blackout came as tensions remained high over Pyongyang’s alleged role in a cyberattack on Sony Pictures that destroyed company computers and pushed the studio to cancel the release of a satirical movie about an assassination plot against North Korea’s leader Kim Jong Un.
Websites for North Korea’s Korean Central News Agency, and a major daily newspaper, the Rodong Sinmun, as well as another propaganda website, Naenara, were restored Tuesday morning, suggesting Internet service had returned.
The timing of Monday’s outage caused many to speculate the U.S. played some role in it. But a senior Obama administration official said Monday that the debate about how to respond to North Korea appeared to be continuing, suggesting Washington hadn’t directed the outage.
“We have no new information to share regarding North Korea today,” said Bernadette Meehan, spokeswoman for the National Security Council. “If in fact North Korea’s Internet has gone down, we’d refer you to that government for comment.”
President Barack Obama has said that the U.S. “will respond proportionately” to North Korea over the incident. Options floated for such action include additional economic sanctions and placing North Korea back on the U.S. list of state sponsors of terrorism.
Nevertheless, the outage reflected the murkiness of conflict in cyberspace, where many incidents fall short of war but rise above everyday nuisance. It also demonstrated the variety of actors in cyberwar: While speculation centered on the U.S. and North Korean governments, the operator of a Twitter account linked to the activist group Anonymous claimed credit for the counterpunch. The claim couldn’t be verified.
North Korea’s single known connection to the Internet runs through China United Network Communications Group Co. , or China Unicom . It went dark late Monday morning East Coast time, according to Internet-monitoring and security companies. It remained out late Monday.
North Korea isn’t a hotbed of Internet connectivity—most of its citizens have no access to the World Wide Web—which complicates theories on what did or didn’t happen in light of the Sony breach.
Outside investigators weren’t able on Monday to immediately inspect what was clogging up North Korea’s Internet pipes, and there are no other ways for the few citizens in the North who would have noticed the outage to spread details.
Attackers conceivably could have knocked the country offline by flooding North Korea’s small sliver of the Internet with useless traffic, making it inaccessible for legitimate users. People familiar with the discussions have said the U.S. saw several drawbacks to launching a counterattack against North Korea.
“It’s a little early to say what the explanation is,” said Matthew Prince, chief executive of CloudFlare Inc., a San Francisco security and network company monitoring the outage. Absent the Sony hack, “I would have thought North Korea decided to turn the Internet off for some reason.”
Governments that tightly control information, including Turkey and Syria, often shut access to the outside Web, especially during global tensions.
Another option is that China Unicom could have killed North Korea’s access, experts said. “China could be reminding North Korea who owns ‘the pipes’ it depends on,” said Peter Singer, co-author of the 2014 book “Cybersecurity and Cyberwar: What Everyone Needs to Know.”
U.S. officials have said they are reaching out to China to help respond to North Korea following the Sony hack, but there have been no indications China would be willing to pressure its bellicose neighbor. The U.S. and China have had their own spats over hacking, U.S. officials note.
Secretary of State John Kerry spoke with his Chinese counterpart over the weekend about the attack on Sony. “We have discussed this issue with China specifically in order to share information and express our concerns about the attack and ask for its cooperation,” State Department spokeswoman Marie Harf said.
China Unicom couldn’t be reached to comment.
Doug Madory, a researcher at Dyn Inc., a U.S. Internet company, offered a possible benign explanation: network-router software gone haywire. But he said North Korea’s network is so small that an accidental outage for several hours is less likely.
“This is out of character for North Korea,” Mr. Madory said.
For all the talk about cyberwar Monday, a person familiar with the discussions said U.S. officials are leaning toward a non-cyber response. Cyberattacks, the person said, often “aren’t worth the risk.”
—Carol E. Lee and Julian E. Barnes in Washington and Jonathan Cheng in Seoul contributed to this article.