"There is also a need to lower the temperature and refrain from actions and rhetoric that could further inflame the situation," Annan said.
Pursuing a diplomatic effort, Britain, France, and Germany plan to offer Iran a package expected to include a European light-water reactor and some form of security assurances in return for a halt to enrichment.
The EU trio will discuss their proposal with senior U.S., Russian, and Chinese officials in London next week.
EU officials say security guarantees are the major sticking point affecting their ability to produce a credible package.
European diplomats say only the United States can guarantee Iran's security. But Washington refuses to do so.