John Kerry, en route to Geneva
John Kerry, en route to GenevaFlash90

US Secretary of State John Kerry vowed Wednesday that the United States would not let any deal with Iran become a ploy to buy time to increase its nuclear capability, AFP reports. 

As talks between Western powers and Iran resumed in Geneva, Kerry said: "We will not allow this agreement, should it be reached... to buy time or to allow for the acceptance of an agreement that does not properly address our core, fundamental concerns."

The top US diplomat was speaking after holding top-level talks at the State Department with US Defense Secretary Chuck Hagel and their Australian counterparts.

Kerry said the negotiations continuing in Geneva were the "best chance in a decade... to halt progress and roll back Iran's program."

He was speaking after Prime Minister Binyamin Netanyahu embarked on a visit to Moscow in a last-minute bid to prevent the emerging nuclear deal with Iran, which many critics see as a tactic to allow the Islamic state to clandestinely continue its nuclear weapons program.

"We would all like a diplomatic solution, but it needs to be a real solution," said Netanyahu, adding that this would involve Iran halting nuclear work in the same way as Syria was allowing its chemical weapons arsenal to be destroyed.

Speaking as the talks got under way in Geneva between Iran and world powers, Putin for his part said he hoped that "in the nearest future a mutually acceptable solution is found" to end the crisis.

"As the consultations in Geneva showed, there is a possibility this can be done. I hope that the talks that resumed today in Geneva bring results," Putin said.