There is no proof, just proof by assertion (by Turkey). The article states, "The disclosures have angered the United States by exposing the inner workings of U.S. diplomacy, including candid assessments of world leaders. " If the US even suspected that Israel was behind the leaks, the US-Israel relationship would be harmed.
Wreckage found on Reunion island triggers speculation over missing MH370 (DPA)
from the article: WikiLeaks founder: Netanyahu believes exposé will aid Mideast peace