Israel’s wide-ranging strikes on Friday were the product of years of intense spy craft that enabled Israel to degrade Iran’s defenses while bombing sensitive nuclear targets and killing top personnel, according to three Israeli officials with knowledge of the operations.

It was a multipronged operation that included deploying drones and other weapons smuggled into Iran by Israeli operatives, according to one of the officials and two senior Iranian officials with knowledge of the matter.

Israel also identified and tracked the movements of the key scientists and military officials who were assassinated, including at least four senior commanders.

The effort was planned and carried out jointly by Israeli military intelligence and the Mossad foreign intelligence service, and code named “With the Strength of a Lion,” one of the officials said.

The Israeli and Iranian officials spoke on the condition of anonymity to discuss sensitive intelligence matters. The two Iranian officials said they did not know how or when the weapons were smuggled into the country, as the attack was still under investigation.

Iranian officials have condemned the attack and announced the names of officials who were killed but have not spoken publicly in detail about other aspects of the operation.