Israel is not in violation of international law by having nukes because like India & Pakistan Israel chose not to sign the NPT which is is legally within its rights to do. In 1968 the Shah of Iran did sign and when he did that its like waiving Iran's rights to posses or develop nuclear weapons so by developing nukes now Iran is in violation of the NPT and so it is violating international law. Israel as it hasn't signed is not breaking an international laws so in this case it is legally one law applies to one and a different law applies to the other. Also Israel has never formerly admitted to having nukes a position that the US & arab states that don't have any great desire to develop nukes like Saudi Arabia want it to be not because its trying to fool anybody into believing it doesn't have them because the whole point of a second strike option is that your enemy knows they are there and we will only destroy you if you destroy us first. The refusal to admit or deny is just a diplomatic game that suits everybody.
Clashes between IDF and protesters in Bethlehem and East Jerusalem (Reuters)
from the article: Iran makes five-point proposal to world powers in Baghdad nuclear talks