Ambassadors of the United States, South Korea and Japan meet to discuss North Korea's nuclear tests - Reuters

"We want to make clear to the DPRK that its illegal and destabilizing activities have consequences, and that the international community will not accept these actions as the norm," the U.S. ambassador said.

Last week, the United States called on the UN to impose new sanctions against North Korea over its ballistic missile launches, but China and Russia vetoed the proposal.