North Korea threatened to carry out ultra-harsh military action on U.S. soil Sunday, one day after U.S. President Barack Obama vowed a proportional response against the North's alleged hacking attack into Sony Pictures.

In a follow-up to the FBI's recent hacking accusation against Pyongyang, Obama vowed Friday (U.S time) to "respond proportionally," hinting at retaliatory action over the communist country's alleged hacking attack on the distributor of a controversial movie about North Korea, "The Interview."

North Korea had been suspected of involvement in last month's cyberattack on Sony after the country's repeated warnings against the firm's plan to release the movie, dealing with an assassination plot targeting North Korean leader Kim Jong-un.

"Surpassing the proportional response declared by Obama, (North Korea) will carry out a ultra-harsh war of reaction targeting the entire U.S. mainland, including the White House, the Pentagon,

which are the base of terrorism," the strategy department of the North's powerful National Defense Commission (NDC) said in a statement, carried by the official (North) Korean Central News Agency.

"Our military and people are perfectly prepared to fight with the U.S. in all kinds of war, including a cyberwar," the NDC statement said, adding that anyone who joins with the U.S. will also be subject to North Korean attacks.

Pyongyang also dismissed the FBI hacking allegation, calling it a new fabrication against the country. It has never tried any hacking attack, even on South Korea, the North claimed.

Since the hacking attack on Sony last month, the North has consistently denied any involvement, although it said the attack was a righteous deed.

On Saturday, the North proposed a joint investigation with the U.S. into the hacking allegation as it denied the U.S. charges.  

Earlier this week, Sony ultimately decided to call off the film's release, which had been set for Christmas Day, after hackers threatened attacks on theaters showing the movie. Some large theater chains also decided to pull the film from their screens.

Unidentified hackers have warned that "the world will be full of fear" if "The Interview" is released. They also said, "Remember the 11th of September 2001," referring to the date of deadly terrorist attacks on U.S. soil.

The movie is about two American journalists who land an interview with the North Korean leader in Pyongyang but are then recruited by the CIA to kill him.

Pyongyang had repeatedly condemned the movie as the "most undisguised" sponsoring of terrorism, threatening merciless punishment on the U.S. (Yonhap)