Britain, France and Germany warned on Saturday against moves to “exploit” the Iran nuclear negotiations \- a tacit warning to Russia which is accused of delaying an agreement to gain leverage in its invasion of Ukraine. Negotiators in Vienna said on Friday they had halted talks despite having almost sealed a deal to revive the 2015 Joint Comprehensive Plan of Action (JCPOA) to contain Iran’s nuclear activities. The setback came after Russia said it was demanding guarantees that the Western sanctions imposed on its economy following its invasion of Ukraine would not affect its trade with Iran. …