WASHINGTON — North Korea experienced sweeping and progressively worse Internet outages extending into Monday, with one computer expert saying the country’s online access is “totally down.” The White House and the State Department declined to say whether the U.S. government was responsible.

President Barack Obama said Friday the U.S. government expected to respond to the hacking of Sony Pictures Entertainment Inc., 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.

“We aren’t going to discuss, you know, publicly operational details about the possible response options or comment on those kind of reports in anyway except to say that as we implement our responses, some will be seen, some may not be seen,” State Department spokeswoman Marie Harf said.

North Korea has forcefully denied it was responsible for hacking into Sony.

Doug Madory, the director of Internet analysis at Dyn Research, a company that studies Internet connectivity, said the problems were discovered over the weekend and grew progressively worse to the point that “North Korea’s totally down.”

“They have left the global Internet and they are gone until they come back,” he said.

He said one benign explanation for the problem was that a router suffered a software glitch, though a cyber-attack involving North Korea’s Internet service was also a possibility.

Routing instabilities are not uncommon, but this particular outage has gone on for hours and was getting worse instead of better, Madory said.

“This doesn’t fit that profile,” of an ordinary routing problem, he said. “This shows something getting progressively worse over time.”