"Nothing will be gained by turning our backs on mutually beneficial cooperation. Frankly it is regrettable that Pakistan has decided not to attend the conference in Bonn," Clinton told a news conference in South Korea. Pakistan pulled out of the conference on the future of Afghanistan on Tuesday in reaction to a cross-border attack by Nato that killed 24 of its soldiers and plunged US-Pakistani relations deeper into crisis. "I would express regret and hope that perhaps there can be a follow-up way that we can have the benefit of Pakistani participation in this international effort to try to work a stable, secure peaceful outcome in Afghanistan." Clinton stressed that US officials were making every effort to investigate what she called a "tragic incident". "What is most important I think is that we learn lessons from this tragedy because we have to continue to work together."