Britain has informed a United Nations sanctions panel of an Iranian nuclear procurement network linked to two blacklisted firms, according to a confidential report by the panel.

The existence of such a network could add to Western concerns over whether Tehran can be trusted to adhere to a nuclear deal, due by June 30, in which it will agree to restrict sensitive nuclear work in exchange for sanctions relief.

Talks between six major powers and Tehran are approaching the final stages after they hammered out a preliminary agreement on April 2, with Iran committing to reduce the number of centrifuges it operates and to other long-term nuclear limitations.