Azerbaijan halted a Russian shipment of equipment intended for Iran's Bushehr nuclear power plant, demanding more information for fear of violating United Nations sanctions, officials said Monday. The Russian state-run company Atomstroiexport said one or two trucks carrying the equipment were stopped two weeks ago at the town of Astara, on the Azerbaijani-Iranian border. Agency spokeswoman Irina Yesipova said officials were holding talks with both Azerbaijan and Iran. She said the shipment contained "heat-isolating equipment" essential to the plant's operation and that the holdup was not likely to delay the start-up of the plant, which Russia is building in the southern Iranian port city of Bushehr. She could not give any further details about the precise nature of the equipment. Azerbaijani Foreign Ministry spokesman Khazar Ibragim said his country was seeking more information about the shipment due to fears that it might violate any of the three sets of UN Security Council sanctions imposed because of suspicions Iran is seeking to develop atomic weapons. "Considering the sensitivity of the situation, we need to know all the details in order to know whether the shipment falls under UN sanctions," he said. There was no immediate comment from Iranian officials. Iran is paying Russia more than US$1 billion to build the light-water reactor. Construction has been held up in recent months by disputes between Teheran and Moscow over payments and a schedule for shipping nuclear fuel. Russia delivered the final shipment of uranium fuel in January, and Teheran 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 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 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. The US has also sought Russian cooperation within the UN Security Council to push Iran to comply with council demands to stop enriching uranium. Doubts remain about Iran's intentions. The European Union last week asked Iran to open its secretive program to greater international scrutiny by joining a treaty that would let the US and other nations review Bushehr's safety. Iran has insisted it will continue enriching uranium, saying it needs to provide fuel to another 300-megawatt light-water reactor it is building.