SEOUL, South Korea — Key North Korean websites were back online Tuesday after an hours-long shutdown that followed a U.S. vow to respond to a cyberattack on Sony Pictures that Washington blames on Pyongyang. The White House and the State Department declined to say whether the U.S. government was responsible for the shutdown in one of the least-wired countries in the world.

Internet access to the North's official Korean Central News Agency and the Rodong Sinmun newspaper were working normally Tuesday after being earlier inaccessible, South Korean officials said. Those sites are the main channels for official North Korea news, with servers located abroad.

U.S. computer experts earlier said North Korea experienced sweeping and progressively worse Internet outages. One said the country's online access was "totally down."

President Barack Obama said Friday the U.S. government expected to respond to the Sony hack, which he described as an expensive act of "cyber vandalism" that he blamed on North Korea. Obama did not say how the U.S. might respond, and it was not immediately clear if the Internet connectivity problems represented the retribution. The U.S. government regards its offensive cyber operations as highly classified.

North Korea has denied it was responsible for hacking into Sony. But the country has also called the attack a "righteous deed" and for months condemned the "The Interview." Sony canceled plans to release the movie after a group of hackers made terroristic threats against theaters that planned to show it.

North Korea has promoted the development of science and technology as a means of improving its moribund economy. But access to the global Internet is severely restricted. Mobile phones used on the state-authorized network cannot make overseas calls. The North's Intranet gives access to government-sanctioned sites and works with its own browsers, search engine and email programs, according to South Korea's Unification Ministry.