Israeli Prime Minister Benjamin Netanyahu urged world powers to set a "clear red line" for Tehran's atomic activities and said he was unconvinced the world had the resolve to prevent Iran from obtaining nuclear arms.

Mr Netanyahu's remarks yesterday suggest a growing Israeli impatience with its main ally, the US, and other countries that have been pressing him to give diplomacy and sanctions more time and hold off on a go-it-alone Israeli strike on Iran.

"The international community is not placing a clear red line for Iran and Iran does not see international resolve to stop its nuclear programme," Mr Netanyahu said in remarks to his cabinet.

"Unless Iran sees this clear red line and this clear resolve it will not stop moving forward with its nuclear programme, and Iran must not have nuclear weapons."

Mr Netanyahu did not specifically criticise the US but Israeli officials say they hope for stronger language from Barack Obama on possible US military action.

Mr Obama, who has had a frosty relationship with Mr Netanyahu, has insisted he will not allow Iran to build atomic weapons and that all options are on the table.

On Saturday, Tzachi Hanegbi, an influential Netanyahu confidant, said "the rhetoric of the US president is too vague", adding that Iran was not taking Mr Obama's words seriously. In a US election year, Republican candidate Mitt Romney has also sharply criticised Mr Obama's handling of Iran as too weak.

Tehran says it is refining uranium to fuel a planned network of nuclear power plants so that it can export more of its oil and gas. The US and its allies accuse Iran of a covert bid to develop the capability to make nuclear bombs.

Israel, believed to have the only nuclear arsenal in the Middle East, views a nuclear-armed Iran as a threat to its existence.

Mr Netanyahu has said he will speak out about the dangers of Iran in an address this month to the UN General Assembly in New York. A UN report said on Thursday that Iran had more than doubled the number of centrifuges in its fortified bunker at Fordow since May.

General Martin Dempsey, chairman of the US joint chiefs of staff, has suggested Washington would not be drawn into conflict with Iran should Israel attack. "I don't want to be complicit if they [Israel] choose to do it," he said on Friday.

An Iranian general said yesterday that if Israel were to attack, Israeli officials would be the target of retaliation.