Iranian Foreign Minister Mohammad Javad Zarif said on Thursday he hoped Tehran and world powers would reach a final nuclear deal "within a reasonable period of time" but this would be hard if the other side stuck to what he called excessive demands.

Iran, the United States, Britain, France, Germany, Russia and China reached a tentative framework for a nuclear pact on April 2 but several issues remain unresolved. They have a self-imposed June 30 deadline to arrive at a comprehensive agreement.

"If the other side respects what has been agreed in Lausanne and tries to draft, based on mutual respect, a comprehensive agreement with Iran that is sustainable..., then we can meet any deadline," Zarif said after meeting his Greek counterpart.

"If people insist on excessive demands, on renegotiation, then it will be difficult to envisage an agreement even without a deadline," he said in Athens.

France warned on Wednesday it was ready to block a final breakthrough deal unless Tehran provided U.N. nuclear inspectors access to all installations, including military bases.

Iran's supreme leader, Ayatollah Ali Khamenei, last week ruled out international inspection of Iran's military sites or access to nuclear scientists under any agreement. Iran's military commanders echoed his remarks.

Iranian state television reported on Wednesday that the June 30 deadline might be extended. But the United States said it was not considering an extension despite comments from France and Iran indicating there was wiggle room. Zarif is expected to meet his U.S. counterpart John Kerry in Geneva on Saturday.

"I am hopeful we will reach a final conclusion within a reasonable period of time," Zarif said. "In order to do that people need to be realistic, people need to have their foot in reality, not in illusions."

He said Iran could not accept any solution that is "less than respectful, less than dignified.

"We can only have agreements in which both sides can claim that they have achieved positive results. You need to either win together, or lose together. "Iran, with millennia of history, will not be intimidated."

Issues holding up a breakthrough agreement include the pace of easing Western sanctions imposed on Iran over its disputed nuclear activity, and the extent of monitoring and verification measures to ensure the Islamic Republic could not pursue a clandestine nuclear weapons program.

Iran rejects Western suspicions that it has covertly sought to develop a nuclear arms capability as part of its uranium enrichment drive, saying it seeks only peaceful atomic energy.

By Reuters