A White House official said Thursday that the hacking attack on Sony Pictures is a “serious national security matter” that will be met with a “proportional” response. The U.S. government is still investigating who was behind the hack that eventually led Sony to cancel the theatrical release of “The Interview,” White House press secretary Josh Earnest said, according to NBC News.

"This is something that's being treated as a serious national security matter," Earnest said. The attack, he said, was carried out by a “sophisticated actor,” according to Reuters. Earnest added: “They’re mindful of the fact that we need a proportional response . ... Sophisticated actors, when they carry out actions like this, are oftentimes ... seeking to provoke a response from the United States of America. They may believe that a response from us in one fashion or another could be advantageous to them. We want to be mindful of that, too.”

A senior U.S. official told news outlets, including NBC on Wednesday, that the North Korean government was behind the hacking attacks, and though Earnest would not go into further detail about what the Obama administration plans to do in response, experts say potential options include cyber retaliation and economic sanctions, the New York Daily News reported.

Earnest said the U.S. is “considering a range of options” for responding to the attack, but emphasized that there are “important strategic considerations” at play, according to the Washington Times. “This is a matter that is still under investigation,” he added. “Before we start publicly speculating about a response, it’s appropriate that we allow the investigation to move forward.”

The statements by the White House came after Sony on Wednesday canceled the theatrical release of “The Interview,” starring James Franco and Seth Rogen, in response to threats by the Guardians of Peace hacking group that they would attack theaters that showed the film. "The Interview" had been scheduled to open on Christmas Day.

There had been speculation for days that the hack came from North Korea because the movie centers on a plot to assassinate its dictator, Kim Jong Un.