Israel launched a daylight attack on Tehran on February 28 with US participation, striking near the offices of Supreme Leader Ayatollah Ali Khamenei as smoke rose over the Iranian capital, local and social media reported.

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The first blasts were heard near Khamenei's compound in downtown Tehran at around 9:45am local time, with roads to the area already shut down by authorities before the strikes began, Eqtesad News reported on February 28. Further explosions were subsequently heard in northern and eastern Tehran, as well as in the cities of Isfahan and Qom, according to the same report.

Israeli Defence Minister Israel Katz confirmed the attack, describing it as pre-emptive. "Israel has launched an attack against Iran," he said, without elaborating on targets or scale.

Israeli news outlet Yedioth Ahronoth reported that a number of targeted assassinations had been carried out inside Iran.

The United States is participating in the operation, though the full extent of its involvement was not immediately clear, according to a US official and a person familiar with the operation who spoke to AP on condition of anonymity.

The New York Times cited a US official as confirming that American strikes against the Islamic Republic had begun.

Iran's Civil Aviation Organisation spokesman Majid Akhavan announced the closure of the country's entire airspace until further notice on the basis of a NOTAM, while mobile phone services were also cut.

Sirens sounded across Israel simultaneously, with the Israeli military issuing a proactive alert warning the public of the possibility of missiles being launched toward Israeli territory.

Iranian state television reported the explosions in Tehran without giving a cause.

Witnesses described shop and residential windows blown out along Vasal Street and the intersection of Enghelab Avenue, with BRT lane barriers torn from the ground, indicating the force of the blasts, Eqtesad News reported.

It was not immediately clear whether Khamenei had been in his offices at the time of the strike. He had not been seen publicly in days as tensions with the United States mounted over Iran's nuclear programme.

Iran had warned that American military personnel and bases across the region would be targets for any retaliation. No casualty figures had been released by authorities at the time of publication.

Intellinews team in Iran is currently heading to safe locations and will report soon. 

This story is developing.