WASHINGTON — The sanctions demanded by U.S. officials in response to North Korea's announcement this week that it had tested a nuclear device would focus on closing pathways to proliferation of weapons technology.
But U.S. officials say any such effort would have to focus on the air and land routes through China and Russia that the government in Pyongyang has used in response to American monitoring on the high seas.
Since the 1990s, the Pentagon has used naval ships and aircraft to track and even intercept weapons shipments coming out of North Korea.
"Our folks pay very close attention to the vessels they are using and where they go; we stay on top of this one," Adm. William J. Fallon, the U.S. military's top officer in the Pacific, said last month. "One thing we can't do anything about is the air movement, because it goes over Chinese or Russian airspace. It's up to those countries to do things."
The new United Nations sanctions resolution proposed by the United States would direct all members "to undertake and facilitate inspection of cargo to or from" North Korea. In effect, it would require China to help close the gap in American efforts.
It's a challenge unlike any yet faced by U.S. diplomats and military officials. Until now, nations that have developed a nuclear capability have not viewed their new weapons as potential export commodities, as many believe Pyongyang does.
U.S. intelligence officials said Tuesday that they were still collecting data on Monday's declared blast, and knew little about the device involved. One military official said the Pentagon was awaiting data from its lone WC-135 "sniffer" aircraft, which was stationed at Kadena Air Base in Japan at the time of the North Korean test.
At the U.N., Chinese and Russian diplomats resisted tougher proposals by the Americans and Japanese, and U.S. Ambassador John R. Bolton dismissed a North Korean threat to launch a nuclear-tipped missile if Washington refused direct talks. Diplomats hope for a vote on a response to North Korea by Friday.
Past international efforts to block exports and enforce embargoes have had limited and short-lived success. But North Korea's use of Chinese routes for conventional weapons exports raises the concern that it may attempt to use similar means to transship nuclear technologies.
"In the early days, it is absolutely true that the North Koreans sent both missiles and missile fuel and components to the Iranians and the Syrians by sea," said David Kay, a former U.N. weapons inspector who specialized in nuclear proliferation issues. "But they now know that's not a good way to do it, so most of it goes overland via China."
Kay said that, from China, the weaponry probably is flown to places such as Iran and Syria. North Korea also has sold missile technology to Yemen and Pakistan.
The Bush administration has complained repeatedly that Beijing has not lived up to agreements to stop North Korea's shipments of weapons technologies. In testimony last month before a U.S. government commission, State Department officials said they "remain deeply concerned" over China's lack of commitment to its nonproliferation promises.
Thus far, however, U.S. proliferation concerns have centered on Pyongyang's trade in parts for long- and medium-range missiles. By some estimates, North Korea is the world's dominant exporter of ballistic missiles. An evaluation by the London-based International Institute for Strategic Studies estimated that missile sales had earned the North Korean government hundreds of millions of dollars, making it a significant source for hard currency.
But deliveries of missile components have begun to shrink in recent years as North Korea's traditional customers, particularly Iran, have developed their own capabilities. Experts fear that Pyongyang will view nuclear technology, and nuclear material such as plutonium, as a replacement revenue source.
"The thing that worries most people is actually the export of fissile material itself," Kay said.
"I don't think people are worried at this stage about North Korea sending weapons to Iranians or terrorists," Kay added, "although there is virtually nothing on the face of the Earth that the North Koreans have gotten their hands on that they haven't been willing to sell."
China has let North Korea ship missile parts through its territory and airspace and has exported missile systems to rogue governments itself. But U.S. officials consider Beijing less likely to tolerate North Korean nuclear shipments because such exports could undermine China's status as the only nuclear power in East Asia.
"North Korea is China's neighbor, so they, in a sense, have a more proximate cause for worry than even the United States," State Department spokesman Sean McCormack said.