The N-deal gave Iran sanctions relief in return for guarantees it wouldn't obtain nukes. Israel insists Iran would use revenue from sanctions relief to bolster allied groups. Israel's arch-foe Iran backs Hezbollah, Hamas & the Islamic Jihad militant groups. Iran been ramping-up Uranium enrichment (process can create bomb fuel down the line). Nonprofileration experts say Tehran has enough 60%-enriched uranium for a nuclear bomb.
