New Delhi, June 21 -- Israel's military said on Saturday it struck a nuclear research facility in Iran's Isfahan province overnight and emphasized that it was preparing for the possibility of a "prolonged campaign".

The target of the Israeli airstrikes was two centrifuge production sites, reported news agency AP citing an Israeli military official.

Three senior Iranian commanders were killed in the targeted attacks, said the Israeli military.

Smoke was seen rising from an area near a mountain in Isfahan on early Saturday, where a local official said Israel had attacked the nuclear research facility in two waves, reported AP.

"We've been able to take out a large amount of their launchers, creating a bottleneck - we're making it harder ...