Lawmakers, who say they fear Obama administration negotiators may not take a hard enough line with Tehran regime, are also at work on a separate bill to have Congress approve any final agreement on Iran’s nuclear program, Senator Bob Corker said.

“There’s continual efforts to try to figure out a way for Congress to play a role to strengthen whatever final deal may occur,” the Tennessee Republican senator said.

Republican Senator Mark Kirk and Democratic Senator Robert Menendez are finalizing a bill for tougher sanctions on Iran if there is no final nuclear deal by June 30.

Meanwhile, Senator Tom Cotton said on Tuesday that the United States must cease all appeasement towards the ‘tyrannical’ Iranian regime which is the world’s greatest state-sponsor of terrorism,

Tom Cotton said America should begin with ‘immediate and crippling sanctions’ in place of ‘sham nuclear negotiations’ to make the US military threat more credible.

In a speech at the US Heritage Foundation, he said: “Iran is a radical, Islamist tyrannical regime… that has been killing Americans for 35 years.”

“Iran is at war with the West just as the Islamic State is. While operating a repressive totalitarian state at home, the Iranian regime conducts many of these operations against America and our allies through terrorist proxies, as Iran remains the worst state sponsor of terrorism in the world, according to President Obama’s own State Department.”