Menendez, D-N.J., is chairman of the Senate Committee on Foreign Relations. In his speech, he said negotiations on Iran's nuclear capability "must be reinforced by continuous international commitment to sanctions regime against Iran."
"So while I welcome diplomatic efforts and I share the hope that the administration can achieve a final comprehensive agreement that eliminates this threat to global peace and security, I am deeply, deeply skeptical based upon these 21 years of experience," he said.
Iran insists that its nuclear program is for power generation only. But Menendez argued that Iran wants nuclear weapons as part of its effort to become the major power in its region.
Menendez said sanctions must only be loosened in return for verifiable steps on Iran's part to dismantle its nuclear program.
"It is clear that the only intense, punishing economic pressure influences Iranian leaders," he said.