President of the U.S. Council on Foreign Relations Richard Haass said Friday that the nature and extent of the response to the sinking of the “Cheonan” naval vessel depends on the evidence found.

Haass said in his keynote address at the Korea Vision Forum in Seoul hosted by the Unification Ministry that the South Korean government’s investigation into the incident must find conclusive evidence before Seoul can respond.

He said that although he believes North Korea was behind the sinking of the Cheonan, conclusive evidence must be presented by South Korea before the matter is put before the United Nations Security Council.

He said, however, that if such evidence is not obtained, then that must be accepted and a commensurate response must be taken. Haass emphasized that Seoul must prevent a situation where it needs to defend itself against criticism that it is making unfounded claims.

On the resumption of the six-party talks, Haass said that making progress with the current leaders of North Korea would be difficult.