VIENNA — Western powers are offering Tehran high-tech reactors under a proposed nuclear agreement, but a defiant speech by Iran’s supreme leader less than a week before a negotiating deadline casts doubt on whether he’s willing to make the necessary concessions to seal a deal.

Ayatollah Ali Khamenei on Tuesday rejected a long-term freeze on nuclear research and supported the idea of barring international inspectors from military sites. Khamenei, in comments broadcast on Iranian state television, also said Iran would sign a final deal only if all economic sanctions on the country were first lifted. The preliminary deal calls for sanctions to be lifted gradually after an agreement is finalized.

In Washington, White House Press Secretary Josh Earnest said Wednesday, “What we’re most focused on are the actions, not the words.”

A day earlier, he suggested the talks could go past the June 30 deadline.

In another sign the Islamic Republic may be toughening its stance, Iran’s Guardian Council on Wednesday enacted legislation banning access to military sites and scientists.

Both Washington and the International Atomic Energy Agency – the U.N. monitor of Iranian compliance – say IAEA experts need such access to watch Tehran’s present nuclear programs and to breathe life into a long-stalled investigation of suspicions that Iran worked on nuclear arms in past years.

Graham Allison, who directs Harvard’s Belfer Center think tank, told the U.S. Senate Foreign Relations Committee that Khamenei’s ban on visits to military facilities would be “a show-stopper” for a deal.

The West has held out the prospect of providing Iran peaceful nuclear technology in the nearly decade-long effort to reduce Tehran’s ability to make nuclear weapons. But the scope of the help now being offered displeases critics who say Washington is giving away too much.

Iran denies interest in nuclear weapons and is prepared to make concessions on limits in exchange for relief from economic penalties.