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Israel's air strikes against Iranian nuclear facilities early Friday before a critical round of talks between the United States and Iran may lead to serious consequences and stroke extended conflicts across the region.

The Israel Defense Forces said its operation against Iran's nuclear program and long-range missile capabilities will last several days, The Times of Israel reported.

"We are in the window of strategic opportunities. We have reached the point of no return, and there is no choice but to act now," IDF officials were quoted by the paper.

Explosions took place in early hours in the Iranian capital Tehran, Iranian state TV reported. Damage to other parts of Iran were yet to be confirmed.

"Loud explosions are being heard in different locations of the capital Tehran," state TV said without providing details. Iran's air defense systems were on full alert.

Iran suspended all flights at its main Iman Khomeini airport, state TV said. Earlier, Iranian military officials promised strong countermeasures in case of nuclear facilities being hit.

On Thursday, the chief commander of the Islamic Revolution Guards Corps, Major General Hossein Salami, said during a ceremony in Tehran: "The enemy sometimes threatens us with military action. We have always said—and repeat now—that we are fully prepared for any scenario, under any circumstances."

The US and Iran are scheduled to resume nuclear talks on Sunday, the fifth round, which may prove critical with suggestions of breakthrough.

US President Donald Trump said on Thursday that an Israeli strike on Iran's nuclear sites "could very well happen" but advised against it, saying the possibility of a deal was "fairly close" if Tehran compromises on its atomic ambitions in ongoing talks with the US.

Yet the US Ambassador to Israel Mike Huckabee said in an interview on Thursday that Israel was unlikely to attack Iran without a green light from Washington, which further complicated the situation.