Secretary of State John Kerry vowed Wednesday that the United States would not let any deal with Iran become a ploy by the Islamic republic to buy time to increase nuclear capability.

As talks between western powers and Iran resumed in Geneva, Kerry said the negotiations were the "best chance in a decade ... to halt progress and roll back Iran's program."

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.

"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."

Kerry spoke as Israeli Prime Minister Benjamin Netanyahu was on a visit to Moscow seen as a last-minute bid to influence the emerging nuclear deal with Iran strongly opposed by the Jewish state.

"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 manner that Syria is allowing its chemical weapons arsenal to be dismantled.

The draft interim six-month deal being negotiated in Geneva offers some limited relief to the crippling sanctions against Iran in return for halting parts of its nuclear program, as all sides work for a comprehensive final agreement.

"We have very close consultations with Israel, as we do with allies and partners throughout the world," a US official told reporters in Geneva after negotiators began a new round of talks with Iran.

"The United States and Israel share a common objective, and that is to make sure that Iran does not acquire a nuclear weapon. How we get there, we may have some tactical differences, but our objective is identical," the official added.

US lawmakers have echoed Israeli concerns that Iran could win an easing of sanctions without sufficient brakes on its nuclear program, but the official said that was misplaced.

"The sanctions relief that is being contemplated -- if we get an agreement -- is quite small. It does not undermine in any way the core architecture of our oil, banking and financial sanctions, which have to remain in place until we get a comprehensive agreement," the official insisted.

National security advisor Susan Rice said meanwhile in Washington that the interim six-month deal would win western powers "time and space for a comprehensive negotiation that could resolve Iran's nuclear problem."

"Without this interim agreement, there will be no break on Iran continuing full-steam ahead with its nuclear program while it talks and perhaps drags out talks," Rice said at a speech at Georgetown University.

"This interim step, if agreed, would halt all progress in Iran's nuclear program and roll back its program in some very key respects."