WASHINGTON - US Defense Secretary Jim Mattis played down concerns on Thursday about whether a potential American withdrawal from the Iran nuclear deal would undermine attempts to strike an agreement with North Korea to dismantle its nuclear weapons program."Some people point out that this could impact on the North Korea negotiations. But I would say in that case, in light of Kim's family and himself breaking every international treaty, every agreement they've ever made ... I'm less concerned with that ripple effect right now," Mattis told a Senate hearing. He was referring to North Korean leader Kim Jong Un."I think we need to focus on what is in the best interest of Middle East stability and the threat that Iran poses."