Britain has told a U.N. panel of experts that it is aware of an "active Iranian nuclear procurement network" linked to two Iranian companies.

Two U.N. sources confirm that Britain's warning on April 20 is included in a confidential report by the panel. The sources spoke on anonymity because they were not authorized to discuss it.

The warning names two companies, Iran's Centrifuge Technology Company and Kalay Electric Company, but it gives no details.

The report comes as world powers negotiate with Iran on a possible comprehensive agreement on its nuclear program by June 30.

Iran has not commented on the report. Iran is pushing for U.N. and other sanctions on it to be lifted as soon as a nuclear agreement is reached.