Israel is convinced that if it attacks Iran then the USA will have no choice but to join in. What the Americans are trying to tell them is that *if* the USA jumps in on Israel's side *then* the Russians and the Chinese wight just jump in on the side of Iran. The result won't be the clean dismemberment of Iran that the Israelis are expecting, but instead a very, very messy replay of the Korean War.
Passport control employees at Ben Gurion airport to strike between 11 A.M. and 1 P.M. (Haaretz)
from the article: U.S. army chief heads to Israel as fears over attack on Iran mount