SEOUL, South Korea - Japan said today it wants to press ahead with a search for debris from North Korea's rocket launch in hopes of dissecting the country's missile know-how.

Meanwhile, Republican Sen. John McCain urged China to use its influence to rein in Pyongyang - a call Beijing rejected.

"If we can confirm North Korea's capability to build a multistage rocket and technology to separate it as well as to control its posture and thrust force, that means a possibility that the North's ballistic missile development is progressing rapidly," Japanese Defense Minister Yasukazu Hamada Hamada told lawmakers.

He said, however, that technical difficulties and concerns about cost may make it difficult to renew the search.

Japan sent ships to scour waters about 170 miles (280 kilometers) off the country's northwestern coast for rocket fragments after Sunday's launch.

Initial searches were called off after nothing was found. Besides fragments to the west of Japan, more debris also fell into the Pacific Ocean much farther to the east.

North Korea said the launch successfully put a satellite into orbit, though Japan, South Korea and the United States assert the country was actually testing long-range ballistic missile technology amid fears its eventual aim is to develop the ability to deliver a nuclear warhead.

Japan has been one of the countries most vocal in its criticism of the launch, which marked the second time since 1998 that Pyongyang fired a rocket over the country.

In Beijing, McCain urged China to take a firmer stand against North Korea, arguing it has more leverage than any other country to influence Pyongyang's behavior.

The Arizona Republican said stronger measures were needed in response to the launch, including sanctions at the U.N. Security Council.

"I want to say very frankly what we all know, and that the nation that has true influence over North Korea" is China, McCain told reporters following meetings with China's foreign and defense ministers and the head of its national legislature.

"And we have urged the Chinese to exercise that responsibility as quickly as possible and as strongly as possible, which in my view, they have not done enough of in the past," he said.

McCain, who unsuccessfully ran for president last year, also expressed disappointment at the lack of progress in six-nation talks aimed at shutting down Pyongyang's nuclear programs.

The negotiations, hosted by China and involving the U.S., Japan, Russia and North and South Korea, are stalled over Pyongyang's refusal of a verification process that would confirm it had dismantled its nuclear programs as earlier promised.

China is Pyongyang's strongest ally and has so far offered a muted response to the rocket launch.

"Pressure will not contribute to the goal of denuclearization of the Korean peninsula," Chinese Foreign Ministry spokeswoman Jiang Yu said at a regular media briefing Thursday. "We hope all parties would through diplomatic efforts press ahead with the denuclearization efforts."

Associated Press writers Mari Yamaguchi in Tokyo and Christopher Bodeen in Beijing contributed to this report.