A widespread Internet outage in North Korea that lasted about 9.5 hours appeared to be over late Tuesday after a preliminary look at some North Korean websites. However, it was unclear if all of the nation's Internet connections were back up. The blackout came less than a week after the FBI accused the country of being behind the hack that forced Sony Pictures to cancel the release of 'The Interview.' The Internet blackout began sometime Monday morning Eastern Time, a U.S. official confirmed to NBC News. Two U.S. officials denied any U.S. involvement in the outage. It was not immediately clear what had caused the outage, which came after President Barack Obama promised that the United States would "respond proportionally" to what he said on Sunday was an "act of cybervandalism."

The hack of Sony Pictures by a group calling itself the "Guardians of Peace," or GOP, forced the studio to cancel the planned Christmas release of the action-comedy, which centers around a plot to assassinate North Korean leader Kim Jong Un. While North Korea's elite might be affected by the outage, most of the country's citizens don't have access to the Internet. DYN Research conducts Internet performance tests around the world. It noticed the problem when it could no longer connect to North Korean websites. “It seemed like in the last 24 hours it was getting progressively worse until it went offline,” Doug Madory, director of Internet analysis at DYN Research, told NBC News. Late Monday night, DYN tweeted that North Korean-hosted websites were once again accessible.

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North Korea's Internet restored after 9 hour, 31 minute outage: pic.twitter.com/ZQ3IrRXbyn — Dyn Research (@DynResearch) December 23, 2014

— Hallie Jackson, Robert Windrem, Tom Winter and Keith Wagstaff