Global powers Tuesday offered to resume stalled talks with Tehran over its contested nuclear drive as US President Barack Obama urged proponents of a military solution to give negotiations a chance.

"On behalf of China, France, Germany, the Russian Federation, the United Kingdom, the United States of America, I have offered to resume talks with Iran on the nuclear issue," said EU foreign policy chief Catherine Ashton.

A time and venue still need to be agreed for the talks, added Ashton, who would head what would be an open-ended series of discussions, with no deadline set, should they take place.

In Washington, where Israeli Prime Minister Benjamin Netanyahu wound up a visit dogged by the threat of Iran's nuclear capabilities and intent, Obama urged a peaceful diplomatic solution.

"Iran is feeling the bite of these sanctions in a substantial way. The world is unified, Iran is politically isolated. And what I have said is that we will not countenance Iran getting a nuclear weapon," Obama said.

"We're now seeing noises about them returning to the negotiating table, that it is deeply in everybody's interests, the United States', Israel's, and the world's, to see if this can be resolved in a peaceful fashion.

"And so this notion that somehow we have a choice to make in the next week or two weeks or month or two months is not borne out by the facts."

Netanyahu has warned Israel cannot afford to wait "much longer" for sanctions to work, and said he would "never let my people live in the shadow of annihilation".

British Foreign Secretary William Hague said world powers aim to show Iran their willingness to seek a diplomatic solution "by testing its desire to talk and by offering it the opportunity to respond to our legitimate concerns."

"It is for Iran to seize this opportunity," Hague said in a statement. "It is time for Iran ... to show the world that it wants a peaceful, negotiated solution to the nuclear issue."

France's Foreign Minister Alain Juppe agreed.

"France calls on Iran to seize the opportunity it has been given to escape from the isolation into which it has been plunged by its nuclear programme with military goals," he said in a statement.

"We invite it to work with us towards a rapid diplomatic solution to the crisis arising from its pursuit of sensitive nuclear activity, in violation of its international undertakings, as the last IAEA report made clear."

Western powers suspect Iran is seeking to build a nuclear bomb, a charge denied by Tehran, which says its atomic programme is for peaceful purposes.

A senior EU official speaking on condition of anonymity said exploratory talks were expected "in the coming days" though negotiations proper were unlikely to kick off before Iran's New Year celebrations later this month.

After several failed rounds, "we hope that this time Iran is ready", said the source, underlining that for the first time there was "a clear written commitment by Iran to be willing to address the nuclear issue in talks".

In Istanbul just over a year ago, Iran refused to address questions on its nuclear programme, demanding what diplomatic sources dubbed "pre-conditions", such as the lifting of sanctions.

In a February 14 letter to Ashton, Iran's chief nuclear negotiator Saeed Jalili said Tehran was ready to resume the deadlocked talks at the "earliest" opportunity as long as its right to peaceful atomic energy was respected.

His letter, a long-belated response to one from Ashton in October, came as world powers moved to adopt unprecedented economic sanctions against Tehran, including an EU oil ban due to come into force on July 1.

Sanctions were ramped up in the last months after the UN's International Atomic Energy Agency said in a report it had evidence the Islamic republic appeared to be conducting research on atomic warheads.

Should talks kick off, both sides will look to "confidence-building" measures, with global powers for instance offering to help boost safety at Iran's civil nuclear power stations, or assist Tehran in fighting drug trafficking.

That would be conditional on Iran agreeing to cooperate with IAEA inspectors and offering assurances it is not on the cusp of producing weapons-grade uranium, diplomatic sources said.

In her letter Tuesday to Iran's chief nuclear negotiator Saeed Jalili, Ashon said:

"Our overall goal remains a comprehensive negotiated, long-term solution which restores international confidence in the exclusively peaceful nature of Iran's nuclear programme, while respecting Iran's right to the peaceful use of nuclear energy consistent with the NPT (Nuclear Non-Proliferation Treaty)."