Iran's Al-Alam TV has been showing footage of military exercises
Iran has begun five days of large-scale war games to simulate attacks on its nuclear sites, officials said, warning it will retaliate if provoked.
The head of Iran's air defence said the aim of the exercises was to thwart aerial reconnaissance and air attacks.
Another official warned Tehran would retaliate with a missile strike on Tel Aviv, if it was attacked by Israel.
Iran is under intense pressure over its nuclear programme, which critics say is intended to produce nuclear weapons.
The US and Israel have not ruled out the prospect of a military attack to prevent Iran developing nuclear bombs. Tehran insists its programme is peaceful.
The head of Iran's air defence, Brig Gen Ahmad Mighani, told state media the aim of the war games, which will cover an area of 600,000 sq km (230,000 sq miles), was "to display Iran's combat readiness and military potentials.
IRAN'S NUCLEAR SITES
Iran insists that all its nuclear facilities are for energy, not military purposes
Bushehr: Nuclear power plant
Isfahan: Uranium conversion plant
Natanz: Uranium enrichment plant, 4,592 working centrifuges, with 3,716 more installed
Second enrichment plant: Existence revealed to IAEA in Sept 2009. Separate reports say it is near Qom, and not yet operational
"Due to the threats against our nuclear facilities it is our duty to defend our nation's vital facilities," he said.
Meanwhile, Mojhtaba Zolnoor, an aide to supreme leader Ayatollah Ali Khamenei, warned Iran would respond to any Israeli attack.
"If the enemy attacks Iran, our missiles will strike Tel Aviv," he was quoted as saying by the official Irna news agency.
The commander of the elite Revolutionary Guards' air force wing said Iran's air defence forces would "annihilate" Israeli warplanes if they attacked.
"Their [Israeli] F-15 and F-16 fighters will be trapped by our air defence forces and will be annihilated," Amir Ali Hajizadeh told Iran's Fars news agency.
"Even if their planes escape and land at the bases from which they took off, their bases will be struck by our destructive surface-to-surface missiles."
Deal in doubt
The exercises come as the UN Security Council's permanent members - Britain, China, France, Russia and the United States - plus Germany, urge Tehran to reconsider its rejection of a proposal that would see some of its nuclear material being enriched outside Iran and returned as fuel rods.
The deal - brokered by the UN's nuclear watchdog, the International Atomic Energy Agency - envisages Iran sending about 70% of its low-enriched uranium to Russia and France, where it would be processed into fuel rods for a research reactor in Tehran.
Such a process would prevent Iran enriching uranium to the degree necessary to make a bomb, the UN says.
But Iran has rejected a key part of the deal, seeking further guarantees.
The UN Security Council has called on Iran to stop uranium enrichment and has approved three rounds of sanctions - covering trade in nuclear material, as well as financial and travel restrictions.
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