In a strongly worded statement, Pyongyang called a new set of UN sanctions "the most vicious, unethical and inhumane act of hostility".
Meanwhile, the presidents of the US and China committed to "maximising pressure" on the North through vigorous enforcement of UN resolutions.
Earlier, the US and South Korea carried out joint military exercises.
North Korea fired its latest missile over Japan on Friday. It travelled 3,700km (2,299 miles), putting the US Pacific territory of Guam, which North Korea says it has a plan to target, within reach.