North Korea has blasted South Korea's sending of observers to the U.S.-led military exercise Proliferation Security Initiative.

The Rodong Sinmun, the official daily of the North Korean Workers' Party, said Saturday that the decision is an act of war that seeks to join Washington's ploy to wage a war of aggression.

In a column titled "Dangerous Conspiracy with Invasive Foreign Forces," the paper said Seoul's observation of the PSI drills is "another intolerable criminal act against the Korean people."

On Thursday, the spokesman's for the North's Committee for the Peaceful Unification of the Fatherland also demanded that the South not send the observers to the exercise.

Seoul late last month said it will send a delegation to watch the anti-proliferation drill, but will not take part in or provide materials for support.

The National Security Council has rejected Washington's request to join the exercise in an apparent effort not to anger Pyongyang.

The PSI aims to intercept sea, air or land shipments of WMDs, their delivery systems and related materials flowing to and from countries of "proliferation concern." Around 70 countries participate in or support the initiative.