Azerbaijan said on Tuesday it had detained a Russian shipment intended for the Iranian nuclear power plant under construction at Bushehr due to concerns that it might violate UN sanctions.

Foreign ministry spokesman Khazar Ibragim told AFP that Azerbaijan had stopped the shipment at its border with southern neighbour Iran because Russia had failed to provide detailed information on its contents.

"It was delayed because we need more information about the details of the cargo. The only information we have from the Russian side is that the material is for the Bushehr nuclear plant.

"We need to know whether this material falls under the United Nations sanctions," said Ibragim.

The UN Security Council has imposed three sets of sanctions on Iran over its failure to heed resolutions requiring the suspension of its sensitive uranium enrichment operations.

Russian state-run company Atomstroiexport said in a statement Tuesday that the cargo, held up at the border since March 29, was "in compliance with internationally recognised rules."

"The waybills and other documents accompanying the cargo detained… had been prepared and formalised in accordance with all requirements international trucking companies are expected to meet," Russia's ITAR-TASS news agency quoted the statement as saying.

The company said the equipment on board was not "subject to special control" and said it had received no requests from Azerbaijan regarding the cargo.

Ibragim said a request had been sent to Russian officials for more information but that there had been no reply.

Russia, one of the five permanent members of the UN Security Council, is completing work on Iran's first nuclear power station at Bushehr.

Moscow has relatively close ties with Iran — its southern border is separated from Iran by just a few hundred kilometres of territory in the Caucasus region, which includes Azerbaijan.

Western governments believe Tehran is trying to develop nuclear weapons, but Tehran insists its programme is peaceful and aimed at generating energy.