TEHRAN, Iran (AP) — Iran’s Supreme Leader warned Sunday that any Israeli attack would be answered with a "lightning" response by the Islamic Republic and suggested Iran’s nuclear program cannot be curtailed by Western sanctions.

The remarks by Ayatollah Ali Khamenei echoed previous hard-line positions by Iran, but take on added resonance amid talks with the U.S. and five other world powers. Western leaders hope for a diplomatic accord that would ease concerns about Iran’s nuclear ambitions, while Israeli officials say they leave all options open to try to derail Iran’s uranium enrichment.

The West fears Iran could one day produce weapons-grade material. Khamenei called the claims of a secret weapons program "lies" and repeated Iran’s statements that it only seeks reactors for energy and medical research.

Khamenei put Israel on notice that any military action would bring swift consequences.

"Should they take any wrong step, any inappropriate move, it will fall on their heads like lightning," he warned in a speech marking the 23rd anniversary of the death of his predecessor, Ayatollah Ruhollah Khomeini, the leader of the 1979 Islamic Revolution.

Many military analysts say air strikes alone are unlikely to seriously set back Iran’s uranium enrichment and could touch off a wider conflict in the Gulf, which is the route for about one fifth of the world’s oil.

Instead, the U.S. and Europe have imposed tighter sanctions targeting Iran’s oil exports and its ability to conduct international banking.

"The obstacles enemies are creating in our path won’t have any effect. Sanctions are ineffective. Sanctions can’t stop the Iranian nation from moving forward," Khamenei said at Khomeini’s mausoleum south of Tehran.

"The only effect these unilateral and multilateral sanctions have on the Iranian nation is that they deepen hatred and animosity toward the West in the heart of our people," he said.

Iran has called for the West to roll back the sanctions as a goodwill gesture to move ahead the nuclear talks, which are scheduled to resume later this month in Moscow.

In Baghdad last month, the six world powers — the U.N. Security Council permanent members plus Germany — demanded that Iran stop its most sensitive uranium enrichment in return for incentives such as civilian plane spare parts. Iran’s 20 percent-level enrichment — the highest publicly acknowledged — worries Western leaders because it is far closer to weapons grade than the 3.5 percent enriched material needed for energy-producing reactors.

Iran uses the 20 percent for its medical research reactor for applications such as cancer treatment.

Iran has called for an overhaul of the latest proposals, saying it may consider suspending 20 percent enrichment only if the West commits to lift recently toughened sanctions.

Israeli Prime Minister Benjamin Netanyahu called on world powers last week to push Tehran to stop all nuclear enrichment, remove from its territory all material that has been enriched until now and demolish the underground Fordo enrichment facility near the city of Qom, about 130 kilometers (80 miles) south of Tehran.

Israel views a nuclear Iran as an existential threat because of its frequent calls for Israel’s destruction and support of anti-Israel groups such as Lebanon’s Hezbollah.

Khamenei said Israel is now vulnerable than any other time with pro-U.S. regimes fallen in the Arab Spring, and claimed the U.S. and its allies are concentrating on the Iranian nuclear issue to "cover their own problems."