Russia says Azeri officials at the border with Iran last month halted the heat insulators for the Bushehr nuclear plant, being built by a Russian contractor in southwest Iran.
"We call on the government of the Republic of Azerbaijan to carry out the necessary measures for the delivery of the consignment to the Islamic Republic of Iran," Foreign Ministry spokesman Mohammad Ali Hosseini told a news conference.
Iran has asked Azerbaijan's ambassador in Tehran "to do his utmost so as to deliver the consignment", he said.
"The consignment is within the framework of Iran-Russia cooperation with respect to the completion of Bushehr power plant. There is no ban regarding the consignment."
Azeri customs officials say the cargo needs a special permit which was not supplied.
The United States and Russia say the plant means Tehran does not need to enrich uranium itself. Western nations fear Iran is seeking to master enrichment technology to make nuclear bombs.
Russia has already delivered nuclear fuel under a $1 billion contract to build the Bushehr plant and Iranian officials say the reactor is likely to be started up in 2008.
Iran's ambassador to Azerbaijan, Nasser Hamidi Zare, said Azeri officials had halted the cargo because of "technical problems", the official newspaper, called Iran, reported.
Russia has asked Iran to help resolve the row over paperwork with Azerbaijan or the row would cause delays in commissioning the plant. Work on it was started in the 1970s before the Russian contractor took over the project in the 1990s.
Iranian officials say it is their right to have a domestic enrichment program and insist that their plans are peaceful.
In a separate incident, two Iranians were shot dead by Azeri border forces on the boundary this month. Azeri media, monitored by the BBC, said the two were trying to cross illegally.
Asked about the incident, Hosseini said: "The treatment we saw from the Azeri forces in connection with the two Iranian youngsters is unacceptable and we condemn it. And of course Iranian border forces will follow up on this issue with sensitivity."
(Reporting by Hossein Jaseb, writing by Edmund Blair; Editing by Robert Woodward)
