Kerry warns no Iran deal if concerns left unanswered

Top US diplomat John Kerry warned Wednesday 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 stop Iran acquiring a nuclear bomb, 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.

Hs said he was leaving on Friday for Vienna "and I look forward to finding out whether or not we will give the full-throated definition that this effort deserves."

The world needed not just any agreement but a deal "to guarantee that this is peaceful program. It's that simple."

It will be the first overseas trip for the 71-year-old Kerry since he fell off his bike in late May after a round of talks with his Iranian counterpart Mohammad Javad Zarif and broke his right leg. He is still walking on crutches.

Iran and the six world powers negotiating the deal known as the P5+1 -- Britain, China, France, Germany, Russia and the United States -- have set themselves a June 30 deadline to nail down one of the world's most complicated nuclear non-proliferation treaties.

- Red lines -

It will end a 12-year standoff between the Islamic republic and the West, which has long accused Iran of seeking to develop a nuclear bomb -- charges Tehran denies.

"There is the possibility that we can finish this by the deadline or a few days after the deadline," Zarif said earlier this week as he met his British, French and German counterparts in Luxembourg.

According to the Lausanne framework, Iran will downsize its nuclear activities, slashing the number of centrifuges enriching uranium, which can be used in nuclear power but also when highly purified for a bomb.

It return Iran wants the lifting of a crippling network of US, EU and UN sanctions which have damaged its economy and barred it from world oil markets.

The powers hope the deal will ensure Iran would need at least a year -- compared with a few months in 2013 -- to produce a bomb's worth of enriched uranium material. Tight UN inspections would give ample notice of any such "breakout."

But Iran's supreme leader Ayatollah Ali Khamenei on Tuesday restated his red lines for a deal including the immediate lifting of US and UN sanctions on banking and the economy.

And he refused a key international demand that UN inspectors be given access to military sites to check whether they had been used for the possible development of a nuclear military program.

Kerry dismissed such statements as "not new" and said what would matter was "what is agreed upon within the four corners of a document."