June 16 (UPI) -- U.S. President Trump cautioned Israel against taking out the Iranian Supreme Leader Ayatollah Ali Khamenei as part of its military offensive targeting the country's nuclear program and, potentially, toppling the regime.

Israeli Prime Minister Benjamin Netanyahu reportedly discussed with Trump an opportunity that had opened up for Israel to kill Khamenei, but Trump shut it down, saying it wouldn't be a good idea, three U.S. officials told CBS News on Sunday.

The conversation occurred at an unspecified point over the weekend and after Israel launched its first wave of massive strikes on Iran's nuclear facilities early Friday.

The two leaders have been in close contact since before the crisis and are maintaining almost daily contact, speaking at the beginning of last week, on Thursday, Friday and at the weekend, according to a Washington-based Israeli official.

Israel's four-day wave of airborne assaults, some from covert units operating on Iranian soil, has been concentrated on the country's nuclear development program, military and energy targets and its senior military commanders and top nuclear scientists, 12 of whom have been killed.