In an interview with CNN on Sunday, Obama said his advisers are weighing how to respond in kind to the attack.

　　"No, I don't think it was an act of war. I think it was an act of cyber vandalism that was very costly, very expensive. We take it very seriously. We will respond proportionately, as I said."

　　Obama said his government was considering putting North Korea back on a U.S. list of countries that sponsor terrorism. It was removed from the list six years ago.

　　On the other side, North Korea on Saturday proposed a joint investigation with the US to determine the true culprit.

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　　It warned of "serious" consequences if Washington rejects a probe that it believes would prove Pyongyang had nothing to do with the cyber attack.

　　"We will never pardon those impure elements keen on insulting the dignity of the supreme leadership of the Democratic People's Republic of Korea. If we need to retaliate we will target with legitimacy those responsible for any attack against us, targeting the attackers and their bases, not innocent audiences in cinemas."

　　But the White House rejected the idea.

　　Also on Sunday, a lawyer for Sony Pictures Entertainment called the hacking a "state sponsored criminal attack."

　　The lawyer, David Boies, promised the movie, which depicts a fictional assassination of the North Korean leader, will eventually come out.