The U.S. spy chief said Wednesday he saw the Sony Pictures movie, "The Interview," and he felt that the North Koreans lack "a sense of humor."

Director of National Intelligence James Clapper made the remark during a cyber-security conference at Fordham University in New York, referring to the North's alleged hack on Sony, apparently in anger over the film involving a plot to assassinate leader Kim Jong-un.

"I watched 'The Interview' over the weekend and it's obvious to me that North Koreans don't have a sense of humor," Clapper told the conference, according to news reports.

The film showed that the North Koreans are "deadly serious" to their supreme leader, he said.

Clapper is believed to be the first high-level U.S. official to acknowledge seeing the film.

The spy chief also said the Sony hack was the "most serious" cyber-attack made yet against U.S. interests and warned that the communist nation could continue such attacks.

"This recent episode with Sony has shown that they can get recognition for their cyber-capabilities," he said. "If they get global recognition at a low cost and no consequence, they will do it again and keep doing it again until we push back."

The hacking attack had scared Sony into briefly canceling the film's planned release. But Sony reversed the decision and widely released the movie, reportedly grossing US$31 million in online and cable sales and $5 million at theaters.

Clapper visited North Korea in November to win the relase of two detained Americans. During the trip, he had a dinner with Gen.

Kim Yong-chol, director of the North's Reconnaissance General Bureau, Pyongyang's top spy agency accused of overseeing the cyber-attack.

The FBI has determined that North Korea was responsible for the hack. Last week, the United States announced retaliatory sanctions, blacklisting three North Korean entities and 10 individuals, including the Reconnaissance General Bureau.

But North Korea has flatly rejected accusations of its involvement.

Some private cyber-security experts have raised questions about the FBI's finding, claiming the skills employed in the attacks were too sophisticated for the North. They have raised the possibilities that laid-off Sony employees or others might have been behind the attacks.

Speaking also at the cyber-security conference, FBI Director James Comey said he is sure that the North was the perpetrator in the Sony hack. The hackers "got sloppy" several times and revealed IP addresses that were used exclusively by North Korea, he said. (Yonhap)