Image copyright Getty Images Image caption The film had been due to open during the holiday season

The US has rejected North Korea's claim that it was not responsible for a cyber-attack on Sony Pictures.

North Korea strongly denies carrying out the attack and invited the US to take part in a joint investigation.

A senior US security official said North Korea should instead "admit culpability and compensate Sony".

North Korea strongly objects to Sony Pictures' satirical film, The Interview, which portrays the fictional killing of its leader, Kim Jong-Un.

After the attack and threats, Sony cancelled the Christmas Day release of the film.

Responding to anonymous threats against cinemas, Sony said it was considering releasing it "on a different platform".

The FBI said on Friday that North Korea had carried out last month's cyber-attack, in which script details and private emails were leaked.

The US defended its findings on Saturday, with US National Security spokesman Mark Stroh saying: "We are confident the North Korean government is responsible for this destructive attack."

"If the North Korean government wants to help, they can admit their culpability and compensate Sony for the damages this attack caused," he said.

Image copyright AFP Image caption North Korea says the film hurts the "dignity of its supreme leadership"

Image copyright AP Image caption The cyber-attack has left Sony Pictures reeling from a massive leak of information

On Saturday, the North Korean foreign ministry said: "As the United States is spreading groundless allegations and slandering us, we propose a joint investigation with it into this incident."

"We have means to prove that this incident has nothing to do with us."

The statement said there would be "grave consequences" if the Americans rejected their inquiry proposal.

The Interview saga

22 November : Sony computer systems hacked, exposing embarrassing emails and personal details about stars

: Sony computer systems hacked, exposing embarrassing emails and personal details about stars 7 December : North Korea denies accusations that it is behind the cyber-attack, but praises it as a "righteous deed"

: North Korea denies accusations that it is behind the cyber-attack, but praises it as a "righteous deed" 16 December : "Guardians of Peace" hacker group threatens 9/11-type attack on cinemas showing film; New York premiere cancelled

: "Guardians of Peace" hacker group threatens 9/11-type attack on cinemas showing film; New York premiere cancelled 17 December : Leading US cinema groups say they will not screen film; Sony cancels Christmas-day release

: Leading US cinema groups say they will not screen film; Sony cancels Christmas-day release 19 December : FBI concludes North Korea orchestrated hack; President Obama calls Sony cancellation "a mistake"

: FBI concludes North Korea orchestrated hack; President Obama calls Sony cancellation "a mistake" 20 December: North Korea proposes join inquiry with US into hacks.

The Interview features James Franco and Seth Rogen as two journalists who are granted an audience with Mr Kim. The CIA then enlists the pair to assassinate him.

The film's cancelled release drew criticism in Hollywood, with some calling it an attack on the freedom of expression.

Sony says it made the decision after most US cinemas chose not to screen the film, following the threats.