Iran Nuclear Agreement Opens 'Window of Possibility,' John Kerry Says

Negotiators have three months to write down the technicalities of a deal.

“This is the most extreme and intrusive inspection structure of an arms control agreement. We have entirely new mechanisms to be able to gain access, to be able to inspect, to hold accountable what is happening in the years ahead," Kerry said in an interview with ABC News Chief Foreign Correspondent Terry Moran. “Those people who criticize it like that, they don't have an alternative."

Kerry concedes that Iran could still try to cheat, despite the agreement, "but we believe we have an ability to be able to know that," he told Moran. The deal could also still fall apart, Kerry concedes.

"Of course it could [fall apart]. It could. What we did was open a window to a possibility,” Kerry said.

"Such a deal would not block Iran's path to the bomb. It would pave it. It would increase the risks of nuclear proliferation in the region and the risks of a horrific war," said Netanyahu. "The alternative is standing firm and increasing the pressure on Iran until a better deal is achieved."

President Obama tried to reassure critics saying the deal was not based on trust but based on unprecedented verification.

Kerry pointed out that the aim of the agreement was never to eliminate Iran's nuclear capabilities.

"They have one, they already have it. Long before I became Secretary of State and before Obama became President. They had a nuclear program and guess what? They were already enriching,” he said.

Sanctions on Iran will remain active until a final deal is drafted and announced on June 30.