Japan has dispatched ships and planes to monitor North Korea amid regional jitters about a possible long-range missile launch, but played down the nation's capacity to possibly load a nuclear warhead atop its rockets.

"At this point, we have encountered no information that indicates North Korea has the technology," said Senior Vice Foreign Minister Yasuhisa Shiozaki. "It requires tremendous technology to miniaturize an atomic weapon in order to load into a missile warhead."

Also speaking at a parliamentary committee meeting on terrorism, Defense Agency chief Fukushiro Nukaga confirmed that his agency had deployed naval ships and patrol planes to monitor developments in North Korea, as the country apparently prepares to test a long-range missile believed capable of reaching the United States.

Nukaga did not elaborate on the monitoring effort, but Japanese media said his agency has sent a destroyer with advanced reconnaissance equipment and an attack aircraft loaded with radar-jamming electronics.

"We have deployed naval ships and patrol planes to maximize our information gathering effort," Nukaga said. "But we do not have accurate information, including details of its technology."

Intelligence reports have said the North is possibly fueling a Taepodong-2 missile with a range experts estimate could be up to 15,000 kilometers (9,300 miles) - making it capable of reaching parts of the United States.