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Iran has ended up with the better part of the international deal calling for a lifting of some sanctions imposed on the Islamic nation, said Sen. Robert Menendez, the chairman of the Senate Foreign Relations Committee.

The New Jersey Democrat said Iran was unreliable and could not be trusted to adhere to the deal's requirements regarding its controversial nuclear program.

“In my view, this agreement did not proportionately reduce Iran's nuclear program for the relief it is receiving. Given Iran's history of duplicity, it will demand ongoing, on the ground verification,” he said in a statement quoted by The Hill. “Until Iran has verifiably terminated its illicit nuclear program, we should vigorously enforce existing sanctions.”

Menendez said he is ready to work with colleagues on beefed-up economic sanctions against Iran "should the talks falter or Iran fail to implement or breach the interim agreement."

Congress is out of town through the end of the month, but lawmakers are already weighing their options for how to address the deal with Iran, in which Tehran agrees to a six-month pause in its nuclear program in exchange for eased sanctions worth $7 billion. Lawmakers from both parties are skeptical the agreement will prod Tehran to give up its nuclear ambitions and say they will be waiting with even harsher punishment if Iran proves an untrustworthy partner.

"I expect that the forthcoming sanctions legislation to be considered by the Senate will provide for a six month window to reach a final agreement before imposing new sanctions on Iran, "Menendez said, according to The Hill, "but will at the same time be immediately available should the talks falter or Iran fail to implement or breach the interim agreement.”

"It is my fervent hope that this interim agreement leads to a final agreement with Iran that will ensure that it cannot acquire nuclear weapons capability.”

Arizona Sen. John McCain said he was "concerned this agreement could be a dangerous step that degrades our pressure on the Iranian regime without demonstrable actions on Iran's part to end its pursuit of a nuclear weapons capability."

The Republican said the situation "would be reminiscent of our experience over two decades with North Korea" and it is essential to keep the pressure on Iran.

Sen. Chuck Schumer, D-N.Y., who is a member of his party's leadership, says he expects the deal "makes it more likely that Democrats and Republicans will join together and pass additional sanctions when we return in December."

And Sen. Marco Rubio, R-Fla., adds: "There is now an even more urgent need for Congress to increase sanctions until Iran completely abandons its enrichment and reprocessing capabilities."

The White House says imposing new sanctions now would undermine international talks, but hasn't issued a veto threat.

In an early Sunday morning announcement, Tehran agreed to pause its nuclear program for six months while diplomats lead talks aimed at preventing Iran from developing a nuclear weapon. While talks continue, international observers are set to monitor Iran's nuclear sites.

But the announcement, after months of secret face-to-face talks between the United States and Iran, left many U.S. lawmakers deeply doubtful of the most significant agreement between Washington and Tehran in more than three decades of estrangement.

House Majority Leader Eric Cantor on Monday assailed the new nuclear deal with Iran, saying he believes it "bodes very, very ominously for the region and U.S. security." In an appearance on "CBS This Morning," the Virginia Republican called the arrangement "dangerous" and said it brings Iran "closer to becoming a nuclear power."

Cantor said the terms of the new deal with Iran are easier than those already contained in several U.N. resolutions. In a twist on a famous President Ronald Reagan statement in the 1980s about arms control deals with the Soviet Union, Cantor said the attitude of the U.S. toward Iran should be to "mistrust and verify." Reagan famously said he favored arms pacts with Moscow as long as there was a "trust-but-verify" standard.

At the White House, Obama's deputy national security adviser, Tony Blinken, said Monday that because the deal gives weapons inspectors "daily access to the most important facilities" in Iran — including "where they make and assemble centrifuges" and mine uranium — it will be easier "to detect whether they're cheating or breaking out or have a covert program." He spoke on CNN.

Sen. Ben Cardin, D-Md., said, "Congress, I think, will want to make it clear that if Iran does not live up to these commitments, we will not only insist that the sanctions be reapplied, but we will have stronger sanctions against Iran."

Distrust that Iran was negotiating in good faith was a common fear across political parties that are otherwise deeply divided. And ready-to-go sanctions seemed to have rare bipartisan support across both of Congress' chambers.

The House in July passed its latest round of sanctions against Iran with backing from both parties but the measure stalled in the Senate.

President Barack Obama pressured Senate leadership to hold off consideration of the measure while negotiators pursued an agreement. Senate Democratic leader Harry Reid of Nevada agreed but said his chamber would take up new sanctions in December, with or without an agreement with Iran.

The Senate returns to work Dec. 9 and lawmakers already were talking about sanctions designed to caution Iran that failure to use the six-month window to reach a deal would only leave Iranians in worse economic straits.

Washington has sought to apply economic pressure to Iran since protesters seized the U.S. embassy in Tehran in 1979 as part of the Islamic Revolution. An escalating series of penalties followed, eventually crippling Iran's economy and putting pressure on the nation's middle class. Many of those economic penalties are set to remain in place during the six-month negotiating window announced Sunday.

"If Iran does not consent to a comprehensive agreement that ensures it cannot acquire a nuclear weapon, there is a broad consensus in Congress to impose even tougher sanctions," said Sen. Carl Levin, D-Mich., who is chairman of the Senate Armed Services Committee.

Rep. Mike Rogers, who chairs the House intelligence panel, was more critical of a deal he said aids "the leading nation-state of terror."

"We have just rewarded very bad and dangerous behavior," said Rogers, R-Mich.

While several of the lawmakers issued statements on Iran, Cardin spoke with "Fox News Sunday" and Rogers was on CNN's "State of the Union.

The Associated Press contributed to this story.

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