The United States urged North Korea on Monday to refrain from menacing actions after the communist nation threatened "toughest counteraction" against the U.S. in response to Washington's accusations the North was responsible for a recent cyber-attack on Sony Pictures.

"We do urge North Korea to exercise restraint, to refrain from further threatening actions at this time," State Department deputy spokeswoman Marie Harf said at a regular press briefing.

Harf also rejected the North's demand that the U.S. apologize for linking the North to the hack.

"As the FBI and the president and everyone who's now made clear, we are confident the North Korean government is responsible for this destruction attack. We stand by this conclusion," she said.

"The government of North Korea has a long history of denying responsibility for destructive and provocative actions, and if they want to help here, they can admit their culpability and compensate Sony for the damages that they caused," she added.

On Saturday, the North's powerful National Defense Commission issued a statement denying its alleged involvement in the hack on Sony and vowing to boldly take "our toughest counteraction" against "the White House, the Pentagon and the whole U.S. mainland."

North Korea had been suspected of involvement in the Sony hack because the communist nation has expressed strong anger at a comedy film, "The Interview," which tells about the story of two American journalists recruited by CIA to assassinate North Korean leader Kim Jong-un.

Sony ultimately canceled the planned Christmas Day release of the film.

The FBI announced Friday it determined the North was responsible for the attack. President Barack Obama vowed to "respond proportionally" to the attack and said the U.S. would consider re-listing Pyongyang as a state sponsor of terrorism.

On Monday, U.S. media outlets, including The New York Times, reported that North Korea's links to the Internet went completely dark after days of instability amid speculation the disruption could be the result of a U.S. retaliatory attack.

The paper quoted Doug Madory, the director of Internet analysis at Dyn Research, an Internet performance management company, as saying that North Korean Internet access first became unstable late Friday and the situation worsened over the weekend, and by Monday, the North's Internet was completely down.

State Department deputy spokeswoman Harf said she cannot confirm the reports but added that the U.S. is weighing a range of options as to how to respond to the North's cyber-attack as President Obama has said.

"We aren't going to discuss, you know, publicly operational details about the possible response options or comment on those kind of reports in any way except to say that as we implement our responses, some will be seen, some may not be seen," she said. (Yonhap)