ANKARA (Dispatches) -- Iran said talks with France, Germany and Britain on Thursday on its nuclear program were "promising" but more work was needed to settle the 12-year standoff, the official IRNA news agency reported.
Political directors from Iran and the three European countries held talks in Istanbul in an effort to overcome the remaining gaps on a long-term nuclear deal by a self-imposed June 30 deadline.
"The talks were very useful, positive and promising but still we are not in a position to say we made progress," IRNA quoted senior Iranian nuclear negotiator and Deputy Foreign Minister Abbas Araqchi as saying after the talks.
"While discussing details ... we face more diversity of views," he added. "We can reach an agreement if all the parties involved show strong political will to end this issue."
Negotiators from Iran and six major powers failed to meet a self-imposed deadline in November to clinch a final agreement.
Under a Nov. 24, 2013 accord with Britain, China, France, Germany, Russia and the United States, Iran halted its most sensitive nuclear activity and took other steps in exchange for some easing of economic sanctions.
But on Thursday, the U.S. Senate Banking Committee approved a controversial measure that would ratchet up sanctions on Iran.
 Senators voted 18 to 4 to advance the so-called Kirk-Menendez bill.
"It is clear that further action is necessary to compel Iran to reach an acceptable agreement, which is why I strongly support this critical bill," committee chairman Senator Richard Shelby said after the vote.
President Barack Obama's administration says it is opposed to any congressional action that might scupper the ongoing landmark negotiations between international powers and Iran.
Some U.S. lawmakers insist on keeping Iran’s feet to the fire by pressing ahead with a deferred sanctions bill before June 30, which would trigger a gradual escalation of economic sanctions beginning in July should talks collapse.
But in a victory for Obama, senators on Tuesday agreed to delay a full Senate vote until at least March 24 to allow international negotiators to reach a political framework agreement without congressional pressure.
In order to be ready to launch such a debate on the Senate floor after that date, the Banking Committee finalized the bill's text Thursday, a procedural requirement that served to revive the threat of new sanctions.
Currently, 35 of the Senate's 100 members officially back the bill, a figure that is expected to increase in coming months.
On Tuesday, ambassadors from France, Britain, Germany and the European Union met in Washington with Senate Democrats urging them to ease the pressure.
"Let's give time to the negotiations," French ambassador Gerard Araud posted on Twitter, recalling that while the March 24 date was a "goal" the true deadline for an agreement remained June 30.
If Congress passes the final Kirk-Menendez bill, Obama is expected to veto it.