Iran will treat any American attack as the "start of war" and Tehran will respond by striking the "heart of Tel Aviv", a senior political adviser to Iranian supreme leader Ayatollah Ali Khamenei has warned.
The warning came as Iran's Islamic Revolutionary Guard Corps prepared to host naval drills in the sensitive Strait of Hormuz. The state-run Press TV channel said the two-day live-fire exercises would begin on Sunday.
Belligerent exchanges of remarks between Washington and Tehran have escalated in the past week. On Wednesday, US President Donald Trump warned Iran that it faced a "far worse" attack than last year's strikes unless it begins talks over its nuclear programme.
On Thursday, Tasnim news agency said the Iranian military had received a batch of 1,000 drones. "In accordance with the threats ahead, the army maintains and enhances its strategic advantages for rapid combat and imposing a crushing response against any aggressor," army chief Amir Hatami said.
From the American side, USS Abraham Lincoln carrier strike group has arrived in the Middle East, meaning Washington has major firepower within range of Iran. Shipping trackers on Thursday showed a further US destroyer, the USS Delbert D Black, heading to the region.
The US previously threatened to launch an attack over the Tehran regime's deadly crackdown on nationwide protests.
"Any military action by the US from any origin and at any level will be considered the start of war and [the] response will be immediate, all out and unprecedented, targeting the heart of Tel Aviv and all those supporting the aggressor," Ali Shamkhani said on X on Tuesday.
Iranian Foreign Minister Abbas Araghchi also warned that Tehran would respond forcefully to any attack, but did not rule out a new nuclear deal.
Fears of war initially eased when Mr Trump held off from carrying out strikes in support of anti-regime protesters in Iran. But concerns have not gone away, with some Middle East flights being rerouted or suspended due to the high tension.
Russia is ready to evacuate its staff from Iran's Bushehr nuclear power plant if necessary, the head of it state nuclear corporation, Alexei Likhachev, said on Thursday. President Vladimir Putin said last year that hundreds of Russians were working at the facility, Iran's only operating nuclear power plant, which Moscow built.
A Turkish Foreign Ministry source told Reuters that Mr Araghchi would visit the country on Friday for talks with Foreign Minister Hakan Fidan on the tension with the US. Mr Fidan has said Ankara opposes any foreign intervention in Iran and urged Washington to resolve its issues with Iran "one by one".
The US and Iran had been engaged in negotiations aimed at reaching a nuclear deal, but talks were derailed in June last year when Israel launched strikes on Tehran. The US attacked Iranian nuclear sites during the 12-day war. Since then, Tehran has been cautious about returning to the negotiating table.
The American aim in the nuclear talks is to prevent Iran from developing a nuclear bomb. Tehran has long maintained it has no intention of doing that, but its stockpiling of enriched uranium - at levels close to weapons-grade - have sent alarm bells ringing in foreign capitals.
A deal was struck in 2015 to lift sanctions on Iran in exchange for limits being placed on its enrichment activities. But Mr Trump withdrew from that agreement during his first presidency, after which Iran openly flouted the curbs it had agreed to.
Iranian authorities have blamed the recent nationwide protests and related deaths on “foreign-backed” rioters, accusing the US and Israel of inciting violence and unrest. More than 6,300 people have been killed in the demonstrations, the US-based Human Rights Activists News Agency said.
Mr Trump said he held back from ordering military action against Tehran after being told protest killings were easing and plans for large-scale executions had been halted.
