The United Kingdom, France and Germany have agreed to restore tough U.N. sanctions on Iran by the end of August if there has been no concrete progress on a nuclear deal, two European diplomats said Tuesday, Associated Press reported.

The three countries’ ambassadors to the United Nations met Tuesday at Germany’s U.N. Mission to discuss a possible Iranian deal and reimposing the sanctions. The matter also came up in a phone call Monday between U.S. Secretary of State Marco Rubio and the foreign ministers of the three countries, according to two U.S. officials.

The State Department said after the call that the four had spoken about “ensuring Iran does not develop or obtain a nuclear weapon.”

The officials and diplomats spoke on condition of anonymity to discuss private conversations, according to Associated Press.