TEHRAN, Iran (AP) — Iran will redesign its Arak heavy water reactor to greatly limit the amount of plutonium it can make, the country’s vice president said Saturday, marking a major concession from the Islamic Republic in negotiations with world powers over its contested nuclear program.

The comments by Vice President Ali Akbar Salehi come as the talks face an informal July 20 deadline to hammer out a final deal to limit Iran’s ability to build nuclear arms in exchange for ending the crippling economic sanctions it faces.