Defense officials said the United States was ready to use its missile defense system if necessary against any threatening launch.

"If such a launch takes place, we would seek to impose some cost on North Korea," Peter Rodman, US assistant secretary of defense for international security affairs, told a Congress committee.

A North Korean missile test "would be a provocation and a dangerous action which would have to have some consequences." He told lawmakers "there would be a reaction, and it would be a mistake for North Korea to do it."

South Korea's Defense Minister Yoon Kwang-ung said in Seoul that he did not believe a missile operation was imminent, but North Korea has received new warnings against making a launch.

North Korea's ambassador to Moscow, Pak Ui Chun, was summoned to the Russian foreign ministry and warned that firing a missile would threaten regional stability, the ministry said in a statement.

Preparations for the launch of a multi-stage Taepodong-2 with a range of up to 6,700 kilometers (4,200 miles) have been underway for several weeks at Musudanri on the remote northeast coast of North Korea. US reports have said a launch was imminent.

North Korea in 1998 fired a long-range Taepodong-1 over Japan into the Pacific Ocean and last year said it would no longer keep to a moratorium on launches.

Stephen Hadley, the US national security adviser, said President George W. Bush wanted to solve the crisis diplomatically and called on North Korea to stick to the moratorium.

Hadley, travelling with Bush in Hungary, warned that a missile launch would be "disruptive" to stalled six-nation talks aimed at convincing the North to drop its nuclear weapons ambitions. North Korea has boycotted the talks since November.

US Vice President Dick Cheney said however that North Korea's missile capability was not state-of-the-art. He also said a diplomatic settlement should be pursued.

In a Washington Post opinion piece co-authored with a former Pentagon official, ex-defense secretary William Perry called for an ultimatum for North Korea to put away the missile or face a US missile strike to destroy it.

Perry and co-author Ashton Carter said that "intervening before mortal threats to US security can develop is surely a prudent policy."

But Cheney told CNN in an interview, "I think, at this stage, we are addressing the issue in the proper fashion."

He added: "And I think, obviously, if you're going to launch a strike at another nation, you'd better be prepared to not just fire one shot."

At the same time, Cheney said that "North Korean missile capabilities are fairly rudimentary" and that "their test flights in the past haven't been notably successful.

A senior US defense official, who spoke on condition of anonymity, said the US military would use any capability it has if a missile is launched at the United States.

However, he said the US missile defense system would not necessarily be used if a missile launched by North Korea was headed into open ocean.

His comments were the clearest official indication yet that the United States has activated its missile defense system which has been developed at a cost of tens of billions of dollars since the 1980s.

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