The United States is “deeply concerned” about North Korea’s nuclear advances, a senior US official said after a US research institute predicted Pyongyang could possess as many as 100 nuclear weapons within five years.

North Korea could be almost ready to carry out its threat to conduct a nuclear test, a US research institute said, pointing to recent satellite photos.

North Korea has stopped construction on a launch pad where intercontinental-range rockets could be tested, according to an analysis of new satellite imagery.