Kerry, Biden to brief top Senate Democrats as Iran sanctions mulled U.S. Secretary of State John Kerry will brief Senate Democrats Wednesday on the latest round of talks with Iran. Biden and Kerry will brief Senate Democratic leaders on Iran nuclear talks They'll be joined by chief negotiator Wendy Sherman and a top Treasury official Kerry will also talk to members of the Senate's Banking Committee That committee may propose new Iran sanctions; one GOP senator says he will Washington (CNN) -- Vice President Joe Biden and Secretary of State John Kerry will be among those briefing Senate Democratic leaders Wednesday on talks about Iran's program, which have picked up significantly in recent months after years of bitter stalemate. Chief negotiator Wendy Sherman and David Cohen, under secretary for terrorism and financial Intelligence at the Treasury Department, will join Biden and Kerry, according to sources familiar with the planned meeting. The closed-door briefing it set to happen Wednesday afternoon, the sources said. It comes in addition to another private meeting that Kerry will hold Wednesday with members of the Senate's Banking, Housing and Urban Affairs Committee, chaired by South Dakota Democrat Tim Johnson. These discussions come during a fast-moving time when it comes to Iran, as diplomatic talks to address the Middle Eastern nation's nuclear program advance at a relative breakneck pace while some in Congress continue to push for more punitive sanctions against Tehran. Three intense days of discussions involving top diplomats -- including Kerry, European Union foreign policy chief Catherine Ashton and Iranian Foreign Minister Mohammad Javad Zarif -- concluded early Sunday without an agreement, though numerous key players indicated that things were moving forward. "A lot of concrete progress has been achieved, but some differences remain," Ashton told reporters in Geneva, Switzerland. Added Zarif: "I think we are all on the same wavelength, and that's important. The next day, Tehran signed a deal with the International Atomic Energy Agency agreeing to give the U.N. nuclear watchdog agency's inspectors access to long-unseen nuclear sites, including a heavy-water reactor in Arak. This pact signified a new willingness by Tehran to cooperate with the IAEA, its director general told CNN's Christiane Amanpour. "The atmosphere is very different, the meeting was very constructive," Yukiya Amano said. Yet some in Washington still don't trust Iran's leaders and are reluctant to ease sanctions that have wounded that nation's economy, led to slashed crude oil exports and triggered problematic inflation. Some of those restrictions originated in the Senate's Banking Committee that Kerry will address Wednesday. Senators from both parties have pushed for toughening sanctions -- not weakening them -- to increase pressure on Iran even given the seemingly promising talks. Johnson won't decide whether he'll move forward a proposal for more sanctions until after this week's briefing and talks with his colleagues, an aide with the banking committee said. But Sen. Lindsey Graham, a South Carolina Republican, told CNN's "State of the Union" program Sunday that he would not wait for the next round of negotiations. A member of the Foreign Relations Committee, Graham said he intends to propose a measure that would mandate more sanctions, aimed at forcing Iran to dismantle its nuclear program -- a move that runs counter to interim steps sought by negotiators in Geneva. CNN's Ted Barrett reported from Washington, and CNN's Greg Botelho wrote this story from Atlanta.