Israel's unprecedented strikes on Iran, which have killed top military leaders and nuclear scientists, required years of meticulous intelligence gathering and infiltration, experts say.

Israel said it hit hundreds of targets on Friday alone, and has since continued its attacks, striking a defence facility and fuel depots on Sunday.

The fiercest-ever exchange of fire between the arch foes came in the midst of ongoing talks between Tehran and Washington seeking to reach a deal on Iran's nuclear programme.

"Israel has been following the nuclear programme for 15 years," Israeli analyst Michael Horowitz told AFP.

"The strikes we see are the result of years of intelligence gathering and infiltration of the Islamic republic."

Israel has previously carried out more limited attacks against Iranian military sites, including in October last year.

"It seems that this week's operation had been in preparation for months, with an acceleration after the operation last year significantly weakened Iranian air defences," Horowitz said.

The United States and other Western countries, along with Israel, accuse Iran of seeking a nuclear weapon.

Tehran denies that, but has........

© Al Monitor