South Korean President Park Geun-hye pledged on Tuesday further "strong" measures against North Korea, after suspending operations at a jointly run industrial park as punishment for the North's recent long-range rocket launch and nuclear test.It was time to face the "uncomfortable truth" that the North would not change, Park said in comments that mark a significant reversal for a leader whose policy on Pyongyang had been based on what she'd described as "trustpolitik" that she hoped would lay the ground for eventual unification.Park said past efforts at engagement had not worked. "It has become clear that the existing approach and goodwill are not going to break the North Korean regime's nuclear development drive," she told parliament.Washington and Seoul are seeking support from Beijing, Pyongyang's main ally, for tougher sanctions against North Korea for the Feb. 7 rocket launch and January's nuclear test."The premise of 'trustpolitik' was that the North was a partner. The president's comments in effect mean that premise was wrong. It is a complete turnabout in North Korea policy," said Hong Sung-gul, a political science professor at Kookmin University.South Korea last week suspended the operation of the Kaesong industrial zone, which had been run jointly with the North for more than a decade. The industrial park was a key source of hard currency for the impoverished North.