Iran's Bushehr plant is said to be nearing completion
Azerbaijan has allowed a Russian cargo of nuclear heat-isolating equipment to cross into Iran after holding it up for a month, Azerbaijani officials say.
The cargo for the nuclear plant Russia is building at Bushehr had been waiting at the border since 29 March as Baku demanded details of its contents.
Russia's state-run nuclear company had insisted the contents were not subject to any special controls.
It is believed the equipment is being carried in a vehicle convoy.
Russia delivered its first shipment of nuclear fuel to Bushehr in December and the plant is due to go into operation this summer.
While the United Nations Security Council has imposed sanctions on Iran for failing to halt uranium enrichment, it has approved the Russian deliveries.
Some Western countries fear oil-rich Iran is trying to build nuclear weapons. Tehran insists its programme is for peaceful power generation only.
Azerbaijan said it had detained the cargo to determine whether it breached UN sanctions.
BUSHEHR NUCLEAR PLANT
Begun in 1974 with German assistance
Work halts after Iran's 1979 Islamic revolution
Resumed in 1992 with Russian help
13 Dec: Russia and Iran agree to finish plant after numerous delays
Two pressurised water reactors
One believed near completion, could begin operating within months
It was released after Moscow sent the necessary information, said Azerbaijani foreign ministry spokesman Khazar Ibragim.
"We received the information from Russia, studied it and then we decided to let it go," he was quoted as telling AFP news agency.
The shipment entered Iran through the Astara customs checkpoint.
Iran first planned a reactor near the south-western port of Bushehr with German assistance in 1974.
Those plans were abandoned after the Islamist revolution in 1979 but the Russians picked up the project in 1992.
On 13 December, Russia and Iran agreed on a schedule to finish construction on the Bushehr plant after repeated delays.