Israel's prime minister has accused the international community of failing to draw a "clear red line" for Iran over its nuclear programme, after a UN report found Tehran had doubled its capacity at a nuclear site.

"I think that we should speak the truth -- the international community is not drawing a clear red line for Iran," Prime Minister Benjamin Netanyahu said at the start of his weekly cabinet meeting on Sunday.

"Iran doesn't see determination from the international community to stop its nuclear programme," he added.

"Until Iran sees this clear red line and this determination, it won't stop advancing its nuclear programme. Iran must never be allowed to acquire nuclear arms."

The comments are Netanyahu's first since the details of a new report from the International Atomic Energy Agency (IAEA) emerged on Thursday.

The report said that Iran has doubled its uranium enrichment capacity at the underground Fordo facility, in spite of UN Security Council resolutions, sanctions and talk of Israeli military action.

The UN nuclear watchdog also said that its ability to inspect the Parchin military base where it suspects Iran conducted nuclear weapons research in the past had been "significantly hampered" by a suspected clean-up.

The report showed that Iran now has around 2,000 uranium-enrichment centrifuges installed, compared with around 1,000 in May, at the Fordo facility.

Enriched uranium can be used for peaceful purposes but in highly concentrated levels of purity it can also be used for nuclear weapons, and multiple UN Security Council resolutions have called on Iran to suspend enrichment.

White House spokesman Jay Carney, speaking to reporters aboard Air Force One, insisted there was "absolutely no daylight between the United States and Israel when it comes to the necessity of preventing Iran from acquiring a nuclear weapon."

US President Barack Obama "has been engaged in a policy that has put enormous pressure on the regime in Tehran, isolated it and sanctioned it to a degree that is unprecedented," he added.

Carney alsp reiterated that the "window" for solving the nuclear standoff through diplomacy remained open but warned that it would not remain open indefinitely."

However Netanyahu said that the IAEA report confirmed what he had bee saying for a long time: "The international sanctions may be weighing heavily on Iran's economy but are not hindering the advancement of Iran's nuclear programme."

He added that Tehran was using talks with world powers "to buy time" to advance their nuclear programme."

Iran has held several rounds of talks with the P5+1 group of world powers comprising Britain, China, France, Russia and the United States, but the negotiations have so far led nowhere, with a fresh round due "in the the coming days," EU officials said last week.

Israel, the Middle East's sole, if undeclared, nuclear power, has led the international charge to pressure Tehran to halt its nuclear programme.

The Jewish state and much of the international community believe Iran's nuclear activities mask a weapons programme, a charge Tehran denies.

Israel has said it considers Iranian nuclear weapons an existential threat and has consistently warned it retains all options, including military action, to prevent Iran from obtaining such arms.