Israel launched a missile strike on Iran less than a week after Tehran’s rocket and drone barrage, according to two US officials. 

An explosion was heard Friday in Iran’s central city of Isfahan, the country’s semi-official Fars news agency reported, as concerns mounted about Israeli retaliation.

Flights were suspended in Isfahan and the Iranian cities of Tehran and Shiraz as well as airports across the country’s western borders, Iran’s Mehr news agency also reported. 

The cause and details of the blast are unknown, according to Fars, but Isfahan — home to several military bases and facilities — is believed to have been one of several launch sites for Iran’s April 13 attack. 

Israeli officials had notified the US earlier Thursday that they planned to retaliate in the next 24-48 hours, according to two US officials who asked not to be identified discussing private conversations. Spokespeople for the National Security Council and the Pentagon declined to comment.

Brent crude jumped above $90 a barrel and gold surged past $2,700 an ounce on the reports. US bond yields fell across the curve, with the 10-year yield down 10 basis points at 4.53%

The reports come after Israel vowed to retaliate against Iran for its barrage of some 300 drones and missiles. Iran said it was responding to a strike on its diplomatic building in Syria that killed several Iranian officers on April 1. 

Iran has been bracing for retaliation by Israel ever since. World leaders from the Mideast to the US have urged Prime Minister Benjamin Netanyahu to show restraint in the face of the Iranian attacks, but the Israeli leader and other top officials have said the country would have little choice but to respond. 

Tehran has routinely accused Israel of attacks and sabotage activities targeting its nuclear and military sites in the past, including in Isfahan, home to some of its key nuclear enrichment and missile facilities.

Read more: What Are Israel’s Options for Retaliating Against Iran’s Strike?

Any missile or drone strike on Iranian soil, no matter the target, would be a significant move for Israel. But it wouldn’t necessarily be the first attack in Iran by Israel. Former Prime Minister Naftali Bennett said Israeli forces destroyed a drone base in Iran in 2022 under his orders.

In an interview with CNN on Thursday night Iranian Foreign Minister Hossein Amirabdollahian warned against retaliation for the weekend assault. “In case the Israeli regime embarks on adventurism again and takes action against the interests of Iran, the next response from us will be immediate and at a maximum level,” he said.

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