The US has a policy of no assassination of civilians. They do assassinate terrorist combatants and their senders since they participate in a "war". If the US did assassinate the Iranian scientist, this would have been a foolish departure from policy, because killing scientists is just too easy, especially scientists in democracies. I hope it isn't true, but if the Iranians are correct, the authorizing US official should pay the price.
Passport control employees at Ben Gurion airport to strike between 11 A.M. and 1 P.M. (Haaretz)