North Korea on Saturday warned of nuclear war and vowed to strengthen its deterrent forces, as it demanded that Washington show evidence backing its allegation that the communist regime is counterfeiting US money. "Dark clouds of a nuclear war are hanging low over the Korean Peninsula," the North's official Rodong Sinmun newspaper said in a commentary carried by the state-run Korean Central News Agency. "The ever-more frantic moves of the US to ignite a new war against (North Korea) would only compel it ... to bolster its deterrent for self-defense in every way," it said. The North has repeatedly accused the US of planning to attack. Washington has denied any such intention.