Seoul, South Korea (CNN) -- "Troubling and counterproductive" rhetoric from North Korea is inflaming tensions on the Korean peninsula, but ultimately, "we will judge North Korea by its actions, not its words," the U.S. envoy to North Korea said Friday.

In its latest bout of saber-rattling, North Korea on Friday warned of the possibility of "strong physical counter-measures" against South Korea after the United Nations imposed tougher sanctions against the North earlier this week.