The comments by Mohammad Javad Zarif came after President Barack Obama's Democrats last week staved off a united Republican effort to sink the July agreement in Congress.
"We hold the US government accountable for the implementation of the JCPOA," Zarif told a press conference in Tehran, referring to the Joint Comprehensive Plan of Action agreed with the six powers, including Washington.
"In our view, any measures in violation of JCPOA by Congress should be stopped by the United States government," he said.
Republican lawmakers have vowed to press on with their campaign to torpedo the deal despite Thursday's blocking vote in the Senate.
They have threatened legal action against the administration, claiming that by failing to provide lawmakers with the texts of what they call "side deals" -- confidential inspection protocols negotiated between Tehran and the UN nuclear watchdog -- it breached its obligations to Congress.