Top US diplomat John Kerry warned there would be no deal with Iran if it fails to satisfy all lingering questions about its nuclear program, as he prepares to head back to tough negotiations. Firing the starting gun on what is set to be the last phase of a gruelling diplomatic marathon to ensure Iran’s peaceful nuclear program, the State Department announced Kerry would be leaving on Friday for Vienna. "It may be that the Iranians will not fill out the full measure of what was agreed on in Lausanne, in which case there will not be an agreement," Kerry told reporters. He was referring to the parameters of a deal to stop Iran getting a nuclear bomb agreed on April 2 in Switzerland, under which Tehran pledged to cut back its nuclear activities in return for a lifting of international sanctions. Whether or not Iran can satisfy the world that its nuclear program is entirely peaceful "will be determined in the last days, by whether or not the outstanding issues that we've been very clear about are in fact addressed," Kerry said. "If they are not addressed there won't be a deal," the US secretary of state stressed again. This is while, Iran’s supreme Leader also last week emphasized on the country’s redline and declared that Iran will never seek atomic bombs, however will not agree with the deal if the conditions are not met.