The Israeli air force has carried out a strike on Iran, according to US news site Axios, which cited two sources with knowledge of the operation.

Explosions were heard northeast of the capital Tehran early on Friday, reported Iran's state-run Nour News.

Israel's defence minister has announced a "special situation" in his country and said schools would stay shut on Friday.

Sky's Middle East correspondent Alistair Bunkall said people in Israel were woken in the early hours by air raid sirens and a phone alert warning there could be "severe retaliation".

A statement from defence minister Israel Katz said: "Following the State of Israel's pre-emptive strike against Iran, a missile and drone attack against the State of Israel and its civilian population is expected in the immediate future."

Bunkall said it appears so far that Israel is acting alone.

It comes amid fears over Iran's nuclear programme, with a warning this week that it's not complying with its obligations for the first time in 20 years.

Israel and the US have long feared the aim is to develop a nuclear weapon, something Tehran has repeatedly denied.

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