The government's top negotiator to the six-party nuclear talks says Seoul has left open a window of opportunity for North Korea to build a light water reactor in the future.

Song Min-soon told reporters Thursday before the talks that Seoul knows what Pyongyang wants and is discussing procedures and methods to help the North reach its goals.

Stressing flexibility as essential to the talks, he said South Korea is exercising flexibility and expects the same from the other parties.

On whether the term "light water reactor" will go into a joint statement, Song said the term's inclusion in the statement is not important, stressing the North’s opportunity to build the reactor later remains open.