“It is past time for the Iranians to take the concrete steps that would reassure the world that their nuclear program is, as they claim, exclusively peaceful,” wrote 44 senators in a Friday bipartisan letter organized by Sens. Robert Menendez (D-NJ) and Roy Blunt (R-MO). “Absent these steps, we must conclude that Tehran is using the talks as a cover to buy time as it continues to advance toward nuclear weapons capability. We know that you share our conviction that allowing Iran to gain this capability is unacceptable.”

The senators wrote that the “absolute minimum” Iran must do immediately to justify further talks is to shut down the Fordo uranium enrichment facility near Qom, freeze all uranium enrichment above 5 percent, and ship all uranium enriched above 5 percent out of the country.

“We understand that this was the very proposal that the P5+1 advanced during the Baghdad meeting,” the senators wrote, referring to the permanent five members of the U.N. Security Council plus Germany. “Were Iran to agree to and verifiably implement these steps, this would demonstrate a level of commitment by Iran to the process and could justify continued discussions beyond the meeting in Moscow.”