Investigators from the United States think that North Korea may have received outside help in last month's huge cyberattack from Sony Pictures. Now a prominent Republican senator seems to agree with that notion.

Sen. Lindsey Graham (R-S.C.) told CNN that he thought China was involved in the North Korean cyberattack. He called for more U.S. action against the hermit kingdom so they can "feel the pain that is due."

"I can't imagine anything this massive happening in North Korea without China being involved or at least knowing about it," Graham said on CNN.

According to CNN, he called for more sanctions against the regime and for President Barack Obama to list North Korea as a state sponsor of terrorism again. In a rare moment, he praised the president's handling of the North Korean brouhaha so far.

"So far so good, Mr. President," Graham said.

Mark Hosenball and Jim Finkle of Reuters reported that the cyberattack on Sony Pictures has been the most destructive against a company on U.S. soil. That's because the hackers stole large amounts of data, wiped hard drives, and brought down the studio's network for more than a week.

While U.S. investigators think that Pyongyang may have "contracted out" some of the dirty work, the FBI told Reuters that North Korea was still responsible in the end.

"The FBI has concluded the Government of North Korea is responsible for the theft and destruction of data on the network of Sony Pictures Entertainment," the FBI said in a statement.

According to Reuters, North Korea has denied any involvement in the hack attacks and has vowed to "hit back" against any U.S. retaliation.

However, there are some experts within the private security industry who questioned whether or not Pyongyang was behind the cyberattack. Reuters reported that consulting firm Taia Global thought the attacks originated from Russia based on a linguistic analysis, while cybersecurity firm Norse thought it was an inside job by someone who knows Sony well.

"I think the government acted prematurely in announcing unequivocally that it was North Korea before the investigation was complete," Mark Rasch, a former federal cybercrimes prosecutor, said. "There are many theories about who did it and how they did it. The government has to be pursuing all of them."

The FBI still stood by its initial assessment, which placed the blame on North Korea.

"There is no credible information to indicate that any other individual is responsible for this cyber incident," the FBI said.

Regardless of who was behind the unprecedented cyberattack, the South Carolina senator thought it was a wakeup call to show how vulnerable the country was to cyberattacks.

"What's happened here it shows how exposed we are in America to cyberattack," Graham said. "If North Korea can do this to a major corporation in America, what can other people do to our country?"