"We're looking foward to a resumption of the dialogue," Bildt said when asked for comment on a recent agreement to restart long-stalled talks between six world powers and Tehran.
"I don't expect there will be a quick resolution of issues because the gulf of mistrust is so enormously deep," added Bildt as he went into talks with European Union foreign ministers. "It will take some time."
But he added: "I sincerely hope that no one wants to blow up the diplomatic process.
"That would be an act of international irresponsibility of the first order," he stressed.
The EU's foreign policy chief Catherine Ashton is heading the talks with Iran on behalf of Britain, China, France, Germany, Russia and the United States.
But a time and venue still need to be agreed.
Western powers suspect Iran is seeking to build a nuclear bomb, a charge denied by Tehran, which says its atomic programme is for peaceful purposes.
After several failed rounds, the last in Istanbul just over a year ago, the powers agreed to resume the talks last month after receiving a written commitment by Iran to address the nuclear issue at the negotiations.
The move to return to negotiations came amid increasing fears of a possible