North Korea on Sunday lashed out at fresh sanctions imposed by the United States in retaliation for its alleged cyber attack on Sony Pictures, criticizing Washington for refusing a proposed joint investigation.

In a Friday executive order US President Barack Obama authorized the US Treasury to place on its blacklist three top North Korean intelligence and arms operations, as well as 10 government officials, most of them involved in Pyongyang's arms exports.

US investigators have said North Korea was behind the attack in November, but some experts have raised doubts about the conclusions of the FBI probe.

North Korea has repeatedly denied involvement and demanded a joint investigation into the attack - a proposal the US has ignored.

The foreign ministry of North Korea said Washington's rejection of the proposal revealed its "guilty conscience." It said the US was using the attack to further isolate North Korea in the international community.

"The policy persistently pursued by the US to stifle the North Korea, groundlessly stirring up bad blood towards it, would only harden its will and resolution to defend the sovereignty of the country," North Korea's state-run KCNA news agency quoted the spokesman as saying.

"The persistent and unilateral action taken by the White House to slap 'sanctions' against North Korea patently proves that it is still not away from inveterate repugnancy and hostility toward North Korea," it said.

The nation is already under sanction following a series of nuclear and missile tests staged in violation of UN resolutions.

The spokesman also said the new sanctions would further push North Korea to strengthen its military-first policy known as Songgun.

The cyber attack on Sony's computers in late November 2014 led to the release over the Internet of information on employees and unreleased films, as well as embarrassing in-house e-mails.

The hackers also mounted threats against Sony over the planned Christmas release of the comedy film The Interview, which depicts a fictional CIA plot to assassinate North Korea's leader Kim Jong-Un.

Pyongyang, which repeatedly slammed the movie as an "act of terror," earlier praised the hacking attacks as a "righteous deed" possibly staged by its sympathizers but denied involvement.

Following the Sony attack, North Korea's main Internet sites suffered intermittent disruptions in late December 2014.

Obama has warned of retaliation against Pyongyang for the alleged hacking, but his administration denied comment on whether it was linked to the outages.