The U.S. State Department says there's a very specific procedure to designating a country as a state sponsor of terror, with specific criteria that need to be met.

State Department spokesman Mark Toner made the comment during a regular press briefing in response to the introduction of legislation by a bipartisan group of U.S. congressmen, led by chairwoman of the House Foreign Affairs Committee Rep. Ileana Ros-Lehtinen, that aims to re-designate North Korea as a terror state sponsor for its provocations against South Korea last year.

Toner said there's a legal process to relisting a country, adding that he is not aware that that's been undertaken.

His statement suggests that it would be difficult to put the North back on the terrorism blacklist unless new evidence emerges that the communist state is involved in terrorist activities.