"We have an agreement that has the prospect of reaching a comprehensive agreement," Iran's Foreign Minister Mohammad Javad Zarif told a meeting of political and business leaders in Davos.
"If someone comes to torpedo (the agreement), I believe (the person or entity) should be isolated by the international community, whether it's the US Congress or anybody else.
"Now is the time for the international community to stand firm against (the threat of new sanctions)that will unravel an extremely important achievement."
Republicans controlling Congress are seeking to shape US policy on Iran by two possible paths.
One tactic envisages adoption of a bill requiring President Barack Obama to submit any nuclear accord reached with Iran to Congress for approval.
Another strategy is based on economic sanctions that would be activated if Tehran refuses to sign a final deal or is seen as violating its terms. The Congress is expected to begin debate on possible new embargoes within weeks.
Obama has threatened to veto any move by Congress to adopt new sanctions.
But Zarif warned that Iran's president did not have similar powers over parliament.
"In our constitution, our president does not have the power to veto parliament (which has) threatened publicly" to take retaliatory action against any move by Congress.
"They will adopt something requiring the government... to increase our (uranium) enrichment," said Zarif.
Any resumption of enrichment would essentially flout an interim accord done between Iran and major world powers in November 2013 offering Tehran partial sanctions relief in exchange for a freeze by Iran of contentious parts of its nuclear activities.
Iran and the so-called P5+1 group -- the United States, Britain, China, France, Germany and Russia -- have been seeking a comprehensive accord that would prevent Tehran from developing a nuclear bomb in return for an easing of economic sanctions.
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Iran says its nuclear program only has civilian aims and that there is no plan to build a bomb.
Two earlier deadlines passed without the final deal and a third deadline is looming on July 1.
A flurry of talks have been held since last week, and Iranian and US diplomats resumed talks in Switzerland on Friday.
ZARIF AND KERRY IN DAVOS
Both Zarif and US Secretary of States John Kerry are in Davos but it was unclear if another round of talks is planned.
The Iranian minister said Tehran is still "prepared to go for a deal" as "confrontation doesn't help anyone".
"There are all sorts of possibilities and I don't want to entertain them because I believe there is a possibility, a very good probability of reaching an agreement and we should not waste that opportunity."
Past negotiations have stumbled over Iran's insistence that it retain the right to enrich some uranium -- which can in some cases be used to make an atomic bomb -- for what it says is its civilian nuclear programme.
There has also been disagreement over global sanctions, with Tehran calling for an end to the crippling regime while the US has insisted on a temporary, gradual suspension.
Zarif on Friday insisted that "the policy of sanctions has not produced positive results".