North Korea has furiously denounced the United States for imposing sanctions in retaliation for the Pyongyang regime’s alleged cyber-attack on Sony Pictures.

North Korea’s foreign ministry reiterated that it did not have any role in the breach of tens of thousands of confidential Sony emails and business files and accused the US of “groundlessly” stirring up hostility towards Pyongyang. He said the new sanctions would not weaken the country’s 1.2 million-strong military.

“The policy persistently pursued by the US to stifle the DPRK [North Korea], groundlessly stirring up bad blood towards it, will only harden its will and resolution to defend the sovereignty of the country,” North’s state-run KCNA news agency quoted the unnamed spokesman as saying on Sunday.

On Friday, the US sanctioned 10 North Korean government officials and three organisations, including Pyongyang’s primary intelligence agency and state-run arms dealer, in what the White House described as an opening move in the response towards the Sony cyber-attack. It was the first time the US has imposed sanctions on another nation in direct retaliation for hacking an American company. Barack Obama also warned that the US was considering whether to put the authoritarian regime back on its list of state sponsors of terrorism.

North Korea expressed fury over The Interview, a Sony comedy about a fictional CIA plot to kill Kim Jong-un, slamming it as an “act of terror”. It denied hacking Sony, but called the act a “righteous deed”.

There have been doubts in the cyber community about the extent of North Korea’s involvement in the hacking. Many experts have said it is possible that hackers or even Sony insiders could be the culprits, and questioned how the FBI could point the finger so conclusively.

Pyongyang has demanded a joint investigation into the attack and claimed US rejection of the proposal was proof of its guilty conscience and that it was seeking a pretext for further isolating North Korea.

“The persistent and unilateral action taken by the White House to slap ‘sanctions’ against the DPRK patently proves that it is still not away from inveterate repugnancy and hostility towards the DPRK,” the foreign ministry said.

The sanctions may have only a limited effect, as North Korea is already under tough US and international sanctions over its nuclear and missile programmes.

The cyber-attack on Sony’s computers in late November led to the distribution over the internet of information on employees and unreleased films, as well as embarrassing in-house emails. The hackers also mounted threats against Sony over the planned Christmas release of The Interview.

The company initially decided to call off its release but, after Obama criticised the decision, Sony authorised its distribution to limited cinemas and also published it online.

Following the Sony attack, North Korea suffered several mysterious internet blackouts last month.

Obama had warned of retaliation against Pyongyang for the alleged hacking, but his administration would not comment on whether it was linked to the blackouts.