IRAN — Iran and six world powers resumed negotiations on its nuclear program on Thursday, the Iranian state news agency IRNA said, seeking to overcome remaining differences with a self-imposed June 30 deadline looming to end a 12-year standoff.

A framework accord was reached between Iran, the United States, France, Britain, Germany, Russia and China on April 2, but several major substantive disputes remain to be resolved including access for U.N. nuclear inspectors to Iranian military sites and the pace and timing of sanctions relief for Tehran.

“We have a few weeks and hope to reach a final deal by the June 30 deadline or even sooner,” IRNA quoted Iranian deputy Foreign Minister Abbas Araqchi as saying after his arrival in Vienna to resume the talks. “There has been progress but still we have a difficult way ahead of us.”

Iranian Supreme Leader Ayatollah Ali Khamenei, who last the say on all matters of state, and Iran’s top military commanders have flatly rejected access to military sites under any deal that would curb the Iranian nuclear program.