Washington (CNN) A top State Department official -- Wendy Sherman -- will depart following the completion of the Iran nuclear talks, a source confirms to CNN. Sherman has been the lead U.S. negotiator with Iran as the Obama administration has pursued a nuclear agreement.

"Wendy has been an absolutely critical member of my team, most notably in her work spearheading the nuclear negotiations with Iran, but on nearly every important issue that has crossed my desk," said Secretary of State John Kerry in a statement provided to CNN.

Sherman, the under secretary for political affairs, is the fourth-ranking State Department official. A key member of Kerry's team, she departed for Vienna, Austria, Wednesday along with the negotiating team to continue the European Union-coordinated P5+1 talks, according to a State Department release.

On Saturday, Sherman is scheduled to join Kerry in Geneva, Switzerland, for further meetings with Iranian officials.