U.S. strikes on Iranian nuclear sites inflicted "serious and significant damage," Iran has acknowledged for the first time since the attack nearly a week ago.

Two Israeli sources told U.S.-based ABC News that calling the operation a success would be premature at this stage, while one source downplayed the damage.

Conflicting claims about the damage to Iran's nuclear program from US strikes have implications for the state of relations between the two countries, including future talks.