WASHINGTON - US President Barack Obama said on Monday it would not be right for Congress to impose new sanctions on Iran now, saying, "Now is the time for us to allow the diplomats and technical experts to do their work."

Raising the issue in comments to reporters, Obama said that if Tehran abides by the agreement, "then I have no doubt that it can open up extraordinary opportunities for Iran and their people."

But if they refuse, he said, then "we are in position to reverse any interim agreement and put in place additional pressure to make sure that Iran does not obtain a nuclear weapon."

Meanwhile, US administration officials lauded the conclusion of technical talks with Iran this weekend, in which international powers agreed after a month of deliberations on how best to implement an interim deal pausing the Islamic Republic’s nuclear program.

“On January 20, when the Joint Plan of Action is implemented, we are going to have the most access we’ve ever had to these sites,” State Department deputy spokeswoman Marie Harf said, calling the start of the deal a “credible, concrete, tangible step.”

The deal freezes Iran’s enrichment of uranium and its construction of a plutonium plant in Arak, in exchange for roughly $7 billion in sanctions relief from the international community.

Over the course of the next six months, the P5+1 – the United States, United Kingdom, France, Russia, China and Germany – will attempt to forge a comprehensive agreement to the longstanding nuclear impasse with Iran.

Talks on a final settlement to the long dispute are likely to begin in February, a diplomatic source said on Monday. The first meeting will include European Union foreign policy chief Catherine Ashton and Iranian Foreign Minister Mohammad Javad Zarif, the source said.

Senior diplomats from the seven countries and the EU will discuss an agenda ahead of the meeting. Ashton herself announced plans on Monday to go to Tehran in the coming weeks in preparation for more talks.

White House spokesman Jay Carney said that US President Barack Obama is “confident” Tehran understands the consequences of failure in the long term, either in upholding the tenets of the interim deal or in reaching a comprehensive agreement.

Such failure, Carney said, “would result in action by the United States.”

The Obama administration voiced concern on Monday about recent reports that Iran and Russia are negotiating an oil-for-goods swap worth $1.5 billion a month, a deal the White House said could potentially trigger US sanctions.

Russian and Iranian sources close to the barter negotiations have said final details are being discussed for a deal under which Russia would buy up to 500,000 barrels a day of Iranian oil in exchange for Russian equipment and goods.

"We are concerned about these reports and Secretary [of State John] Kerry directly expressed this concern with Foreign Minister [Sergei] Lavrov today," Caitlin Hayden, spokeswoman for the White House National Security Council, told Reuters.

"If the reports are true, such a deal would raise serious concerns as it would be inconsistent with the terms of the P5+1 agreement with Iran and could potentially trigger US sanctions," Hayden said.

Of the US Senate’s 100 members, 59 have publicly declared support for a bill that would trigger new sanctions on Iran should six months pass without a final-status accord.

Carney reiterated the president’s opposition to the measure, warning that it could derail negotiations and cause unease among allies.

“Further congressional action, and further international action when it comes to adding more sanctions and new sanctions, would best wait, in our view, if and when Iran fails to meet its obligations or fails to reach a comprehensive agreement with the P5+1,” he said.

Carney said that sanctions should be a “result” of failure.

But members of Congress supporting the measure consider them negative reinforcement, pushing Iran toward peace.

Senator Mark Kirk (R-Illinois), one of the authors of the new sanctions bill, reacted to the conclusion of technical talks on Sunday, calling on his colleagues to support the measure.

“Beginning January 20, the administration will give the world’s leading state sponsor of terrorism billions of dollars while allowing the mullahs to keep their illicit nuclear infrastructure in place,” Kirk said. “I am worried the administration’s policies will either lead to Iranian nuclear weapons or Israeli air strikes.”

Reuters contributed to this report.

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