"A short while ago, the IDF identified missiles launched from Iran toward the territory of the State of Israel," the army posted on Telegram, using the acronym for its official name.

It said its air defences were working to intercept the threat but advised people to "enter a protected space and remain there until further notice".

An AFP journalist heard loud explosions in Jerusalem early Monday, while footage showed Israeli air defences working over the city.

Outside Haifa, an AFP journalist saw fires break out following the latest Iranian barrage.

After decades of enmity and a prolonged shadow war fought through proxies and covert operations, the latest conflict marks the first time arch-enemies Israel and Iran have traded fire with such intensity, triggering fears of a conflict that could engulf the Middle East.

It began Friday, when Israel launched attacks that have killed top military commanders and nuclear scientists, and struck military bases, nuclear sites and residential areas across Iran.