BERLIN (Yonhap News) -- President Lee Myung-bak said Sunday that Korea should seek unification with North Korea at any cost, stressing the need to end Pyongyang's nuclear programs that he said are an obstacle to unification.

Lee made the remark in Berlin, the symbolic city of German unification, on the first leg of a three-nation European tour, saying that unification with the North could come at any time and that he actually believes it "is not far away."

If realized "at any sacrifices, unification will bring about results that boost Korean people," Lee told a meeting with hundreds of Korean residents here. "This is not something we should do calculations about. It will bring much greater prosperity for us."

But making the Korean Peninsula nuclear-free should be a precondition for unification, he said.

"The existence of nuclear weapons on the Korean Peninsula would delay unification. If we are unified with nuclear weapons in possession, neighboring countries won't easily accept it," Lee said. "Though there are various difficulties, I have a firm belief that we have to realize unification."

Lee urged Pyongyang to follow the footsteps of China and Vietnam, open up to the outside world and revive its broken economy. He also said that Seoul is ready for dialogue with Pyongyang whenever the communist regime "comes forward with a sincere heart."

Relations between the two Koreas have been tense since Lee took office in early 2008 with a pledge to link aid to the end of Pyongyang's nuclear programs.

Their ties plunged further last year because of the North's two deadly attacks on the South -- the March sinking of the Cheonan warship and the November shelling of Yeonpyeong Island, which resulted in a combined death toll of 50 people.

The South has demanded the North apologize for the two attacks, but Pyongyang has refused.

"We have been demanding that North Korea must apologize," Lee said. "It should be made to acknowledge its wrongdoing so as to prevent it from committing the same wrongdoing."