The US Senate voted unanimously supporting a non-binding measure to slap new economic sanctions on Iran should it violate terms of any nuclear deal it reaches with world powers.
In a symbolic measure aimed at building pressure on Tehran amid crunch negotiations over its atomic program, lawmakers voted 100-0 on an amendment introduced by Senate Republican Mark Kirk as part of an ongoing budget debate.
It does not carry the weight of law because budget resolutions are not binding legislation, but it signals senators' determination to act quickly should Iran fail to meet any requirements of the interim accord now in place, or a possible final agreement.
With Thursday's vote, the first on the Senate floor since talks began early last year, the measure's author intends to hold his colleagues to account.
"If we find out that there's further development in the Iran nuclear program, it will allow me to remind 100 senators that they voted with me today," Kirk told AFP.
The chamber's entire Democratic caucus came on board after a modification of wording that recognized the role of the US president in making a "determination" about Iran's compliance.
The Senate Foreign Relations Committee votes April 14 on legislation that would require President Barack Obama to give Congress a say on any final deal reached between Iran and the P5+1 -- Britain, China, France, Russia, the United States and Germany.
Congress would have 60 days to review and, if it chooses, ultimately block the deal. The White House is opposed to such legislation, arguing a presidential signature is sufficient.
Kirk and Senate Democrat Robert Menendez have crafted separate legislation that would impose gradual sanctions against Iran should negotiations fail.
The text is on hold, to give the talks a chance to succeed, but Senate leadership is committed to a vote if the talks collapse.
Talks resumed in Switzerland Thursday between US Secretary of State John Kerry and his Iranian counterpart, Mohammad Javad Zarif.
They are racing against the clock to complete the framework of deal by a self-imposed March 31 deadline. A final agreement is due by June 30.
Kirk said Paris's hawkish line on Iran -- notably from French Foreign Minister Laurent Fabius -- has made the senator "a strong ally of the (Francois) Hollande government."
France, Kirk added, "has continually been the clear-headed, realistic nation throughout this process."