"It's something we're following, something we're talking about," the official said, speaking on condition of anonymity. "We're in contact with the Germans abut it."

The weekly Der Spiegel magazine reported this week that Mizan Machine, a company blacklisted by the German authorities, bought a crane to help in the manufacture of Iran's Shahab missile.

It said customs authorities were not told about the deal until the freighter transporting the equipment left Germany. The ship was reported over the weekend to be at the entrance to the Suez Canal.

The US official said Washington was consulting with the Germans as part of the US-sponsored Proliferation Security Initiative, a global effort that aims to intercept shipments of weapons of mass destruction

He said the State Department had conferred with the German Foreign Ministry but added that the United States was seeking "more clarification" at this point rather than action.

Deputy State Department spokesman Adam Ereli would not comment directly on the case, saying only, "We're aware of the reports of this shipment."

"Obviously, when there are indications of incidents of proliferation concern, we take them seriously," Ereli said. "I think that certainly is the case here. We follow it; we try to find the facts."

Iran has denied reports it bought equipment from Germany for its ballistic missile programme, and complained last Sunday that European restrictions were damaging trade with the Islamic republic.

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