Wendy Sherman, the American Undersecretary of State, will lead a delegation to Vienna this Wednesday to join the next round of negotiations on finalizing an Iran nuclear accord, the State Department said Monday, according to AFP.

The American team includes a representative of President Barack Obama’s National Security Council and experts on arms control, non-proliferation, economic sanctions and energy, the report said.

The European Union and Tehran said in a statement last week that the crunch talks aimed at hammering out a final deal by a self-imposed deadline of June 30 were to resume Tuesday in the Austrian capital.

The EU negotiator Helga Schmid and her Iranian counterparts would kick off the talks, with political leaders of the other world powers involved in the negotiations joining in on May 15, last week’s statement said.

The so-called P5+1 group — Britain, China, France, Russia and the United States, plus Germany — is conducting the negotiations aimed at preventing Iran from developing nuclear weapons, in exchange for an easing of punishing economic sanctions.

Iran and six world powers are trying to turn a framework accord reached in Switzerland on April 2 into a full agreement by June 30.

Under the agreed parameters, Iran, which denies seeking the atomic bomb, is set to scale down its nuclear program for 10 to 15 years or more, and allow closer UN inspections.

Tensions arose after the preliminary framework was reached, as Iran recently accused the United States of “fraud” and “psychological warfare” in publishing a fact sheet announcing what the U.S. claims was agreed on in the framework deal and which an Iranian official called a false translation.

Iran’s Supreme leader Ayatollah Ali Khamenei, who will have the final say on any deal, plunged the accord into doubt recently when he suggested that “nothing is binding”, while President Hassan Rouhani demanded that sanctions be immediately lifted when any deal is signed.