It's now been more than a month since Azerbaijani customs officials pulled aside a small convoy of trucks on March 29 at Astara, on the border with Iran, refusing permission for further forward movement of the goods.
The trucks had come from Russia, dispatched on a journey to Iran by the Russian state company Atomstroieksport. They carried 10 tons of equipment destined for Bushehr in southwest Iran, which is being built with Russian help.
Russia has insisted that the shipment's papers are in order, and Iranian officials dismiss suggestions that it might contain banned material.
The director of RFE/RL's Azerbaijani Service, Kenan Aliyev, says the authorities are "not giving the green light," adding that "until Baku decides it's time to let it go, [the shipment] will be staying there."
"The Russian side and the Iranian side are protesting," Aliyev says. "The Iranian Foreign Ministry [on April 28] called on the Azerbaijani authorities to release the shipment [and] the Russians are trying to convince the Azeris that there is nothing wrong with the documentation."
Azerbaijani officials have said special government permission will be needed to release the cargo, which they say consists of heat-insulation material, listed as being worth a mere $171,000. The authorities say they want to be sure that the goods do not fall under UN sanctions imposed upon Iran over its refusal to cease uranium enrichment.
The UN Security Council has approved three rounds of sanctions against Tehran since December 2006.
Iranian President Mahmud Ahmadinejad dismissed the initial package of UN sanctions as a "scrap of paper" and said the international community would have to get used to the idea of a nuclear Iran.
In the latest development over the Bushehr shipment, the Turan news agency quoted sources as saying that the Russian Embassy in Baku has handed the Azerbaijani Foreign Ministry detailed information about the technical characteristics of the cargo.
In Tehran, Iranian Foreign Ministry spokesman Mohammad Ali Hosseini scoffed at the suggestion the insulation is banned material. "The consignment is within the framework of Iranian-Russian cooperation with respect to the completion of Bushehr power plant under the framework of international regulation," he said. "There is no ban regarding the consignment."
Some Russian officials have already dismissed the idea that the paperwork is really to blame, saying they see a "political decision" by the Azerbaijani government to hold up the shipment.
RFE/EL's Aliyev says it is possible that Azerbaijan is trying to show its muscle to its two powerful neighbors. The Azeris have been squeezed for centuries between the Russians and the Persians, and the present Azerbaijan has tense relations with Tehran.
But according to Russian officials quoted by Reuters news agency on April 23, more is at stake than mere political posturing. They say timely delivery of the insulation material is important if the Bushehr construction schedule is to be met. One unnamed official reportedly said it would be "expedient" to find a solution to the problem.
The project to build Iran's first nuclear power plant is already years behind schedule. Work originally started at the site in the 1970s under a German company but later petered out, and since the Russians took over construction there have also been numerous delays.
The United States has long criticized Russia's assistance in the Bushehr project, although President George W. Bush in December expressed support for Moscow's delivery of nuclear fuel to the facility.
Washington recognizes Iran's right to civilian nuclear power, but officials are wary of any development that could help Iran acquire nuclear weapons, which U.S. officials have accused Iran of clandestinely aiming to do.
At the same time, the United States has developed a close relationship with the independent Azerbaijan, which emerged from the breakup of the Soviet Union.
RFE/RL's Aliyev notes Azerbaijan's close ties to the United States and Israel, which President Ahmadinejad has publicly suggested should be "wiped off the map."
"Azerbaijan has close cooperation on border issues with the United States; it's possible that Azerbaijan is cooperating unofficially with the United States," Aliyev says. "But there is no indication that the Americans asked Baku to stop this shipment."
Washington has said little about the wrangle over delivery of the insulation. However, U.S. State Department spokesman Sean McCormack, speaking at a news briefing on April 28, appeared to distance the United States from the cargo dispute.
"In our view, this is something that the Azerbaijani and Russian governments need to work out consistent with everybody's UN Security Council resolution obligations, enforcing those obligations in terms of the transshipment of materials potentially for illicit purposes -- I'm not suggesting that at this point," McCormack said. "So those two countries need to work this out."
The first reactor at Bushehr is nearing completion. Russia has already delivered the nuclear fuel that will fire up the reactor, probably early next year.
THE COMPLETE PICTURE: RFE/RL's complete coverage of controversy surrounding Iran's nuclear program.
An annotated timeline
of Iran's nuclear program.