North Korea claimed on Tuesday that it has deployed "strategic rocket forces" that are able to strike targets in the continental US.
Pyongyang's declaration comes two days after the South Korean government signed an upgraded defence pact with Washington that permits it to develop conventional missiles with a range of 497 miles.
The increased range will enable South Korean missiles to hit targets anywhere in North Korea, although it has provoked anger in both Pyongyang and Beijing, the North's only major international ally.
On Monday, a spokesman for the Chinese Foreign Ministry told a press briefing that Beijing does not want "an escalated military confrontation" in the region and that disputes need to be settled through dialogue.
Quoted by the Korean Central News Agency, the official mouthpiece of the regime, a spokesman for the National Defence Commission said on Tuesday that North Korea is ready to match any enemy, "nuclear for nuclear, missile for missile."
"We are not concealing the fact that our revolutionary military, including strategic rocket forces, have place not only the South Korean enemy forces and US forces in the Korean peninsula, but also Japan, Guam and even the US mainland within its target range," the official said.
Pyongyang carried out the test-firing of a short-range anti-shipping missile on September 27, one day after Lee Myung-bak, the president of South Korea, called on the North to halt incursions by fishing boats across the disputed maritime border on the west of the peninsula.
Five days later, Pak Kil-yon, Pyongyang's vice-foreign minster, warned a meeting of the UN General Assembly in New York that "a spark of fire could set off a thermonuclear war" on the Korean Peninsula.
Pak placed the blame for the heightened tensions on South Korea's conservative government and the US.
North Korea is known to be developing a long-range ballistic missile, but no successful tests have been carried out.
In April, Pyongyang launched what it claimed was a rocket designed to put a satellite into orbit as part of celebrations to mark the centenary of the birth of the founder of the nation, Kim Il-sung. The launch - which the United Nations condemned as a disguised test of a ballistic missile - failed when the vehicle crashed into the sea after being airborne for about one minute.
Spy satellites monitoring movements connected with the launch reportedly identified a new long-range missile as much as 130 feet long - larger than the 105-foot Taepodong-2 weapon - and with a more powerful booster unit. Analysts told South Korea's Chosun Ilbo newspaper that the missile could be capable of delivering a warhead more than 6,200 miles.