“We have been saying for a long time that they can conduct a nuclear test at any time.
In general, I would say that our concern about the possibility of a nuclear test remains high and unchanged, ”TASS quoted him as saying.
Kirby noted that it is "difficult to predict" what exactly could be the "trigger" for testing.
Earlier, North Korean leader Kim Jong-un said he would not enter into dialogue with the United States and the Republic of Korea.
In September, North Korea passed a law on the right to launch a preventive nuclear strike.
Kim Jong Un declared North Korea a nuclear power.