Azerbaijani officials said one or two trucks carrying heat-isolating equipment supplied by the company OAO Atomstroiexport were halted at the town of Astara, on the border with Iran, March 29.
Iranian officials have made no comment about the shipment.
Russia delivered the final shipment of uranium fuel in January, and Tehran has said it was hoping the plant would begin operations by summer. The United States initially opposed Russia's building Bushehr, but later softened its position.
A top Azerbaijani customs official said that release of the blocked equipment, valued at around $170,000, required special government permission. Officials have said they needed assurance the equipment did not violate United Nations sanctions against Iran.
"This cargo consists of isolating materials and falls under the category of cargo that requires expert control," Aidyn Aliev, the chairman of the Azerbijani government customs committee, said in comments televised Tuesday.
Atomstroiexport spokeswoman Irina Yesipova said the company was baffled by the hold-up. She said the government in Baku had not sent a request for more information.
"We do not understand why officials in Azerbaijan are obstructing the delivery," she said.
"Our cargo has been thoroughly inspected and does not fall under U.N. sanctions," she said.
Yesipova could not give any more details about the use of the equipment. It is the first time Atomstroiexport has tried to send cargo through Azerbaijan, she said.
Azerbaijani Foreign Ministry spokesman Khazar Ibrahim said Baku sent the request for information to Russia's embassy soon after the trucks were stopped. He expressed surprise at the company's assertion that it had not received any request.
A spokeswoman for the Russian Embassy would not say whether it had received the request.
Iran is paying Russia more than $1 billion to build the light-water reactor. Construction has been held up in recent months by disputes between Tehran and Moscow over payments and a schedule for shipping nuclear fuel.
The United States changed its position on the Bushehr plant after Iran agreed to return spent nuclear fuel to Russia to ensure it does not extract plutonium from it that could be used to make atomic bombs.
The United States and its Western allies agreed to drop any reference to Bushehr in the sanctions resolutions passed by the U.N. Security Council as a result of Russian pressure. Russia says the plant's contract is in line with all international agreements aimed at preventing nuclear weapons proliferation.
The United States and Russia have said the supply of Russian nuclear fuel means Iran has no need to continue its own uranium enrichment program — a process that can provide fuel for a reactor or fissile material for a bomb. Iran has insisted it will continue enriching uranium.
(Source: International Herald Tribune)