If this week's six-party talks in Beijing make progress in convincing North Korea to end its nuclear weapons program, the task of verifying whether the Pyongyang government has truly disarmed is likely to prove challenging.
The United States, Russia, China, Japan and South Korea are meeting with North Korea to seek an end to the North's nuclear weapons program.
The United Nations' nuclear watchdog, the International Atomic Energy Agency, says a pledge of cooperation would be a good first step in resolving the North Korean nuclear crisis. But Melissa Fleming, spokeswoman for the IAEA, says a final agreement would have to go much further.
"Even more important is legal authority for the IAEA to go beyond what North Korea declares to us and be able to investigate whether there is perhaps secret nuclear activity going on," she said.
Despite previous agreements to end its nuclear programs, North Korea's record on observing international nuclear monitoring standards is not encouraging. IAEA publications say Pyongyang has frustrated and harassed inspection activities since the early 1990s, and point to periods when it is not fully certain how much weapons-grade material may have been processed.
The United States says that in late 2002, North Korea privately admitted pursuing a secret uranium enrichment weapons program. Soon afterward, North Korea ejected nuclear inspectors from its main plutonium-producing nuclear facility at Yongbyon and withdrew from the global Non-Proliferation Treaty.
Earlier this year, North Korea openly declared it had nuclear weapons and said it planned to build more.
Ms. Fleming says any declarations by North Korea about its nuclear disarmament would have no credibility unless matched by unfettered access for inspectors.
"It just wouldn't do much good. No one would feel assured by those declarations by the North Korean side," said Ms. Fleming.
North Korea has never publicly acknowledged having a highly enriched uranium, or HEU, program. But even if it continues to deny the existence of such a program at the six-party talks, Ms. Fleming says an inspection process would have to allow for all possibilities.
"We have suspicious minds, and if there are indications from anywhere that there might be another program, in the case of North Korea, a uranium enrichment program, then we would do everything possible to investigate those suspicions."
Bruce Cumings, a North Korea specialist at the University of Chicago, is skeptical that North Korea, one of the world's most secretive countries, would give inspectors the access they would need.
"The highly enriched uranium processors could be anywhere," he said. "The bombs that they may have produced could be anywhere. So you're going to have to imagine a very wide and verifiable inspection of North Korea, which is hard to imagine."
International organizations have had little success in gaining access to North Korea. Pyongyang has never allowed a specially appointed United Nations human rights researcher to set foot in the country, and the U.N. World Food Program says it is not allowed to deliver aid everywhere it would like.
South Korean officials and other advocates of engagement with North Korea say the six-party talks must adequately address Pyongyang's security concerns, and thereby remove its incentive for operating secret nuclear programs.
But some researchers point out the threat of nuclear weapons is Pyongyang's only leverage in the international community, and it is unlikely to completely dismantle the programs that provide that leverage.
Kim Young-soo, a foreign affairs specialist at Sogang University in Seoul, is blunt about the detective work that awaits any inspectors.
Mr. Kim says inspectors will be looking for packages of weapons-grade nuclear material about the size of a fist and asks: how are they supposed to find them?
IAEA officials say that with enough time and access, they have the technology to know with reasonable certainty whether North Korea is keeping its word on disarmament. Whether that access will be available to them is a question that this week's six-party talks are unlikely to answer.