Iran (at least with its current leadership) would be quite happy to use nukes on Israel if it weren't for mutually assured destruction. As it is having two powers with nukes in a region that despise each other leads to an unstable situation so it would definately be best if Iran did not get it hands on nuclear weapons. (Only Israel having them is an unfair, but stable situation).
North Korea - I have no idea. There is a lot of paranoia in that state and if they managed to convince themselves that they were directly under threat they may well launch nuclear weapons. Kind of how the USSR got extremely close to launching nuclear weapons when a glitch in the system made it appear that they were under attack (which they obviously were not).
I don't think either state should be allowed to get nuclear weapons. Strategic strikes on the facilities (and whatever the consequences) are preferable to setting the world in such an unstable state.
For that matter I don't think any country should have nuclear weapons, out of the countries that do have them the ones that are probably are most dangerous are Israel and Pakistan. Israel because its surrounded by enemies and Pakistan because the state is unstable.
