"The United States and its partners must not draw back on any sanctions against Iran unless all of these conditions are met and implemented," he wrote. "I believe it is in everyone's interest to continue making it clear to Iran's leaders that there are real consequences to supporting terrorism and attempting to develop nuclear weapons."

Schumer said the United States must continue the P5+1 negotiations (the five permanent members of the U.N. Security Council plus Germany) with Iran, but warned that sanctions must be maintained given Iran's "long track record of delay, lies and deception." He also said the international sanctions in place now are working, and that the United States should try to broaden support for these sanctions.

"As you know, international sanctions are having a genuine impact on the Iranian economy, and it is becoming increasingly problematic for Iran to sell its oil on the global market," he wrote. "The rial is severely declining, and the cost of Iran's critical imports continues to escalate. The international community is now more united than ever, but broader support to enact and enforce sanctions is critical."