A Chinese man, an Iranian and two Iranian firms were charged in the United States with conspiring to export devices to Iran that can serve to enrich uranium, an indictment unsealed Friday said.

Sihai Cheng, 34, was arrested on February 7 at London's Heathrow Airport.

London's Metropolitan Police force said Cheng had already appeared at a court in the capital and was awaiting his next appearance.

US prosecutors say Shanghai-based Cheng conspired with Seyed Abolfazl Shahab Jamili of Tehran and the Iranian companies Nicaro Eng. Co. and Eyvaz Technic Manufacturing Co. to export US-made pressure transducers.

The devices, which are a type of sensor, can be used in gas centrifuges to "convert natural uranium into a form that can be used for nuclear weapons," the indictment said.

MKS Instruments Inc. in Andover, Massachusetts produced the parts. According to the indictment, Cheng would ship the transducers to Iran upon receiving them in China.

Publicly available photographs of Iran's Natanz enrichment facility show "numerous" MKS pressure transducers attached to Iran's gas centrifuge cascades, the indictment said.

Cheng began doing business with Jamili and Nicaro around November 2005 and had since sold the Iranian national thousands of Chinese-manufactured parts with nuclear applications, according to US prosecutors.

Jamili, in turn, informed Cheng via email that the customer for the parts was in fact Eyvaz, which was supplying the material to the Iranian government. Cheng subsequently sent the parts directly to Eyvaz at times.

The conspiracy to obtain the MKS pressure transducers began around February 2009 following a query from Eyvaz.

Between April 2009 and January 2011, Cheng then placed orders for more than 1,000 MKS pressure transducers for a value of more than $1.8 million.

Most orders included 30 to 100 units, as Jamili warned Cheng of "critical control condition and boycott by USA government," the indictment said.

Western powers and Israel suspect Iran is covertly pursuing a nuclear weapons capability alongside its civilian program, charges adamantly denied by Tehran.

Iran's oil-reliant economy has struggled under US-led sanctions aimed at curtailing its nuclear ambitions.

The so-called P5+1 group -- Britain, China, France, Russia and the United States plus Germany -- hopes to reach a final accord with Iran by July 20 to lift all sanctions in exchange for Iran scaling back its program to the point where it would be difficult if not impossible to develop nuclear weapons.

Iran says nuclear expert talks 'useful'
Vienna (AFP) April 05, 2014 - Nuclear talks between technical experts from Iran and world powers preparing for a third round of talks next week on a lasting deal were "useful", Iran's lead negotiator said Saturday.

"The technical positions help us to understand better our respective positions," Hamid Baeedinejad told the IRNA news agency after three days of discussions in Vienna.

The meeting came ahead of talks between political directors from Iran and the six powers -- the United States, China, Russia, Britain, France and Germany -- in Vienna from Tuesday, the third such round this year.

These negotiations are aimed at turning an interim deal from November that expires on July 20 into a lasting accord that ends once and for all the decade-old standoff over Iran's nuclear programme.

A senior US administration official involved in the talks said Friday that Washington hoped to begin drafting such an agreement at the following meeting in May.

Baeedinejad said the process would begin in the Iranian month of Ordibehesht, which runs from April 21 to May 21, echoing Iranian Foreign Minister Mohammad Javad Zarif last month.

"We are looking to ensure we have the right combination of measures in place to ensure Iran cannot acquire a nuclear weapon and that its program is exclusively peaceful," the US official said.

"As we work to bridge the gaps that exist to see if we can find that right combination, the pace of our work will intensify even more than it is today."

The official also warned that an oil-for-goods deal reportedly being negotiated between Russia and Iran would be "inconsistent" with the November agreement and "could potentially trigger US sanctions against the entity and individuals involved".

Such a deal between Moscow and Tehran would undermine Washington's efforts to cut off Iran's main source of revenue -- a strategy which the US credits with forcing Tehran to the negotiating table in the first place.

Iran denies seeking nuclear weapons and wants all UN and Western sanctions lifted.