Suspicions that North Korea was behind a destructive hacking attack against Sony Pictures are intensifying calls for tougher US steps to cut access to hard currency and declare it as a state sponsor of terrorism.

James Franco and Seth Rogen in The Interview.

At first glance, US options for responding to the hacking attack are limited. Bringing the shadowy hackers to justice appears a distant prospect.

A US cyber-retaliation against North Korea would risk a dangerous escalation. And North Korea is already targeted by a raft of sanctions over its nuclear weapons program.

"We don't sell them anything, we don't buy anything from them and we don't have diplomatic relations," said William Reinsch, a former senior Commerce Department official who was responsible for enforcing international sanctions against North Korea and other countries.

But the US isn't powerless if it concludes Pyongyang was behind the hack that has prompted Sony to cancel its Christmas Day release of the movie "The Interview."

While US officials are saying privately that they believe North Korea was connected to the attack, the White House has not said so publicly.