President Hassan Rohani has suggested that "many differences over details" remain in talks with world powers on Iran's nuclear activities but added that a deal is "entirely feasible" even if it requires more time.
In a live television appearance, Rohani also said he will not permit commitments under any eventual deal to jeopardize Iranian state secrets.
"Iran will absolutely not allow its national secrets to fall into the hands of foreigners through the Additional Protocol or any other means," Rohani said in a reference to an addendum to International Atomic Energy Agency (IAEA) commitments on inspection authority.
The talks have already been extended once and are facing a self-imposed June 30 deadline.
They have reportedly been stuck on the issue of nuclear inspectors' access to military bases and nuclear sites, possibly including flash inspections on just two hours' notice.
Negotiators from Iran and the so-called P5+1 -- comprising Britain, China, France, Russia, and the United States, plus Germany -- are seeking an agreement to ease international fears over Iran's nuclear program.
In his June 13 comments, Rohani accused the other side of contradicting itself on specifics as they try to hammer out a deal.
"A problem we face on many issues is that when we reach a framework in one meeting, our negotiating partners go back on it in the next meeting," Rohani said, according to Reuters. "If the other side sticks to the framework that has been established, and does not bring new issues into play, I believe it can be solved.... But if they want to take the path of brinksmanship, the negotiations could take longer."
U.S. negotiators have been dogged throughout the negotiations by criticism from ally Israel and political divisions at home, where President Barack Obama's administration has had to fight hard to win time and leeway in pursuit of a deal.
U.S. Secretary of State John Kerry vowed after he was discharged on June 12 from a Boston hospital for treatment of a broken leg that he would be "absolutely, totally, and fully engaged" in the Iran talks and would travel abroad to join them ahead of the deadline.
"Our team is in Vienna right now working out very complex...details of this agreement," Kerry said. "It's a tough slog; it's not easy."
Russian negotiator Sergei Rybakov said as talks in Vienna continued on June 12 that "the rate of progress...is progressively slowing down. He added that "this is very worrying to us, because there is very little time before the deadline."
The United States, Israel, and other governments have expressed fears that Iran is working covertly on a nuclear bomb-making capacity.
Tehran rejects that charge, saying its nuclear program is intended solely for civilian purposes.
But the IAEA has repeatedly warned of Iranian obfuscation, and several rounds of UN sanctions have been passed in an effort to convince Iran to curtail some sensitive nuclear activities, including uranium enrichment.
With reporting by Reuters, dpa, TASS, Ria Novosti, and AFP