The Obama administration has sought to reassure skeptical U.S. legislators that diplomacy can work in international efforts to curb Iran's nuclear ambitions.
Major world powers struck an agreement with Iran November 24 to offer it an estimated $7 billion in sanctions relief in return for steps to restrain Iranian atomic activities. The deal called for negotiation of a full agreement within a year.
On Tuesday, Under Secretary of State for Political Affairs Wendy Sherman, the lead U.S. negotiator with Iran, reassured lawmakers that negotiators will take a hard line on Iran's nuclear program as talks progress.
Members of Congress have argued that it was unwise to ease sanctions before Iran took aggressive action to rein in its nuclear program.
Sherman said that while the deal is "not perfect," it buys time to try to secure a comprehensive deal within a year.
U.S. lawmakers have some influence over Iran policy because of their ability to pass legislation imposing new sanctions on Iran, something U.S. President Barack Obama has opposed during the current negotiations and has threatened to veto.