NEW YORK >> There is strong evidence that North Korea was behind the cyberattack on Sony and that the leadership there will orchestrate further strikes against American targets, top U.S. officials said Wednesday.

An ongoing investigation has found that North Korea had sought to use proxy servers to conceal the Sony hack, FBI Director James Comey said at a cybersecurity conference in Manhattan. But the hackers sometimes "got sloppy" and sent messages that could be traced to IP addresses used exclusively by the North Korean government, he said.

"I have very high confidence about this attribution to North Korea, as does the entire intelligence community," Comey said.

The Sony attack also had "clear links" to malware developed by North Korea, Comey said. The same tools were used in an attack last year on South Korean banks, he said.

Comey said he was hesitant to reveal more about how U.S. officials learned that North Korea was the source "because it will happen again, and we have to preserve our methods and sources."

Earlier Wednesday, Director of National Intelligence James Clapper said North Korea will continue the attacks against American interests unless the United States "pushes back."