UPDATE | US sanctions N. Korea over Sony cyberattack

HONOLULU (AP) — The United States imposed fresh sanctions on North Korea today, targeting the North's defense industry and spy service in an attempt to punish Pyongyang for a crippling cyberattack against Sony.

The sanctions marked the first public act of retribution by the U.S. for North Korea's alleged involvement.

Although it was unclear how painful the blow would be — North Korea already is under tough U.S. sanctions — the move signaled that that the U.S. was not backing away from its insistence that North Korea is responsible for the attack against Sony. North Korea has denied involvement, and some cybersecurity experts say it's possible the North wasn't to blame.

"The order is not targeted at the people of North Korea, but rather is aimed at the government of North Korea and its activities that threaten the United States and others," President Barack Obama wrote in a letter to House and Senate leaders.

Never before has the U.S. slapped sanctions on a foreign nation in direct retaliation for a cyberattack on an American company. But U.S. officials said the North's behavior had "crossed a threshold" that necessitated a swift and decisive response.

The U.S. move also served to put North Korea on notice that payback would not be limited to those who perpetrated the attack. Ten people identified in the sanctions are there because they are associated with the North Korean government, not because of any known involvement with the episode against Sony, Obama administration officials said.