In an article posted on the official Uriminzokkiri website, a member of the Korean National Peace Committee - a propaganda body - said the North was now a "fully-independent rocket and nuclear weapons state".
"The United States should be acutely aware that the US mainland is now well within the range of our strategic rockets and nuclear weapons," the signed commentary said.
North Korea made a similar claim in October last year, saying it possessed rockets capable of striking the continental United States.
That was largely dismissed as bluster, but that was before Pyongyang conducted a successful long-range rocket launch in December, followed by its third nuclear test on February 12.
Although most experts believe the North has a long way to go to developing a dependable inter-continental ballistic missile, the December launch was a strong step in the right direction.
And this month's nuclear test also fuelled concerns that North Korea is refining the technical ability to place a miniaturised nuclear warhead on a long-range missile.
After analysing debris from the rocket launch in December, the South Korean military estimated its possible range at around 10,000 kilometres, bringing in the west coast of the United States.
In a separate commentary today, the Korean Central News Agency (KCNA) slammed upcoming US-South joint military drills, and warned that the Korean peninsula was "an inch away from explosion".