Iran, being a Shia Muslim country, will not be allowed to make nuke weapons by Saudi Arabia the Mahaguru of Sunni Muslims; by throwing a spanner in the works all the time (even instigating/assisting USA to do the dirty work). With Shias comprising of 60% of Iraq's population, a nuclear Shia country (Iran) would be the least welcome thing in Saudi Arabia's (and other Sunni Muslims') scheme of things.
Pakistan being a stooge of Saudi Arabia itself, would not like to see a Nuclear Power Iran.
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Iranian nuke will make Pakistan sad.. Another competitor in the muslim world will remove Pakistan's importance..They always said Muslim Bomb.. Now their bomb will be a cracker only in front of Iran's .. Further, There is no good friendship between Iran and Pakistan..Americans will not like it.. So Pakistan can sing a sad song only..