A top State Department official asked Congress on Thursday to delay further sanctions against Iran until U.S. leaders meet with the country's leaders later this month to discuss the regime's nuclear programs.

Wendy Sherman, undersecretary of state for political affairs, said if Iran's newfound willingness to work with the international community proves hollow, then Congress can and should act.

"I would hope that you will allow us the time to begin these negotiations and see if, in fact, there is anything real here with my telling of the Iranians quite directly that if there isn't, that everyone is ready to act," Sherman said.

Sherman faced a Senate Foreign Relations Committee skeptical of recent rhetoric from Iranian President Hassan Rouhani and Democrats and Republicans unwilling to lift the hardline approach Congress has taken toward the Middle Eastern country. While the newly elected Rouhani has said he would work with the U.S. in exchange for removing some sanctions, trust remains a concern within the State Department and among lawmakers.

"In my personal view, the new face of Iran looked and sounded very much like the old face, with a softer tone and a smoother edge," said committee Chairman Bob Menendez, D-N.J. "Although Iran's messenger may have changed in the last election, the message seems to have remained the same."

Rouhani last week spoke with President Obama over the phone, the first time the two country's leaders have talked since 1979. Diplomats from the two countries are scheduled to meet with five other world powers in Geneva later this month.

"I think we will know when we meet on the 15th and 16th [of October] whether there's anything real here or not," Sherman said. "I think we will know rather quickly whether we are beginning a serious negotiation or whether we are moving down one more road that leads nowhere."

Iran has demanded flexibility to seek peaceful nuclear capabilities for energy needs but insists a weapon is not on the horizon. Evidence in the past has suggested otherwise, and Sherman said a nuclear warhead was likely only a year away.

Rouhani must make substantive and verifiable commitments before the U.S. considers lifting sanctions, Sherman assured.

But others said that might not be enough. Sen. Bob Corker, R-Tenn., noted the country's history of human rights problems and sponsorship of terrorist groups heighten the need for sanctions.

Menendez warned that pulling back sanctions even slightly could be a risk.

"There is a real, legitimate concern here that the Iranians will do a certain amount that ultimately begins to create some sanction relief, but at the end of the day, that draws back the international community; that draws back the forces of keeping the pressure that has brought us to this moment," Menendez said. "And then to gear that back up would be an incredibly difficult proposition."