TOKYO — North Korea, which launched a long-range missile over Japan in April, appeared Saturday to be moving another one to a launch pad.

Reports that a large rocket was moving by train toward North Korea’s east coast punctuated a tense week on the Korean Peninsula. It began Monday with the North’s underground test of a nuclear device, included six short-range missiles fired into the Sea of Japan, and featured a declaration by the government of Kim Jong Il that the truce that ended the Korean War was null and void.

In Singapore at a regional defense meeting, Secretary of Defense Robert Gates signaled that the United States and many of North Korea’s neighbors are getting fed up.

“We will not stand idly by as North Korea builds the capability to wreak destruction on any target in Asia — or on us,” Gates said, according to the Associated Press. He said that he did not call North Korea’s nuclear program a direct threat to the United States but that it was a “harbinger of a dark future.”

Gates told defense officials at the meeting that the U.S. government understands and disdains the game of brinkmanship North Korea is playing.

“They create a crisis, and the rest of us pay the price to return to the status quo ante,” he said. “As the expression goes in the U.S., I’m tired of buying the same horse twice.”

The missile recently spotted on a cargo train resembled the Taepodong II missile that North Korea launched over northern Japan into the Pacific Ocean on April 5, an official told Yonhap, the South Korean news agency.

Yonhap quoted other South Korean officials who said activity had been spotted around a factory in the North known to build long-range missiles.

The long-range launch in April, which violated U.N. resolutions and triggered condemnation from the U.N. Security Council, demonstrated to American experts that North Korea has made significant progress in multistage rocket technology.

If North Korea perfects an intercontinental ballistic missile the size of the Taepodong II, experts say, it may have enough range to strike the western U.S.

In Singapore on Saturday, defense ministers from South Korea and China joined Gates in expressing annoyance at the North’s recent behavior.

Lt. Gen. Ma Xiaotian, the second in command of the Chinese military’s General Staff, said China “has expressed a firm opposition and grave concern about the nuclear test.”