The United States is monitoring North Korean missile preparations on the same launch pad used in the failed 2006 test of a long-range Taepodong-2, but there is no sign of an actual missile, U.S. officials said on Tuesday.

Washington believes Pyongyang is preparing for some sort of launch but may be moving cautiously to avoid a repeat of test problems that caused the Taepodong-2 missile in 2006 to explode seconds after launch at North Korea's Musudan-ri missile test site, the officials said.

"There doesn't appear to be a missile on the pad," said a U.S. defense official. "You're seeing preparations similar to '06. You're seeing some of the same signs. They're using the same launch pad."

A U.S. counterproliferation official agreed that preparations were taking place on the same launch pad but that no actual missile had appeared.

The officials spoke on condition of anonymity because the subject involves classified intelligence.

North Korea said on Tuesday that it was preparing to launch a satellite on one of its rockets, although analysts have said the launch would actually be the test-firing of a Taepodong-2, which is designed to strike U.S. territory.

The U.S. military stepped up its monitoring of the North Korean test site weeks ago by moving assets believed to include Navy ships and high-altitude sensors into position near the Korean peninsula.

Officials were reluctant to say what kind of launch Pyongyang might be readying without seeing a missile.

Meanwhile, U.S. officials and their counterparts in Seoul, Tokyo and Beijing are divided about whether a launch could be expected in days or weeks.

"They'd probably rather be correct than fast," said the U.S. defense official. "But North Korea will do what it wants to do."

North Korea stunned the region when it fired a missile over Japan in 1998, saying it had launched a satellite.

If the long-range rocket flies successfully, Pyongyang would have a missile with a maximum range of 4,200 miles (6,700 km), designed to eventually carry a nuclear warhead that could hit U.S. territory, but not the contiguous 48 states, analysts said.