A Europe-based missile shield proposed by the US against a perceived Iranian threat will not work and should be scrapped, according to a think tank study based on a consensus of US and Russian experts.

Dropping the shield, which Moscow strongly opposes, would make it easier for the US to work with Russia and other big powers to rein in Iran, the New York-based EastWest Institute said.

The study said Iran could develop a basic nuclear device in 1-3 years and a missile-borne nuclear warhead five years after that but there was no proof of such intent and Iran was unlikely to start a nuclear conflict.

Iran, expanding enrichment of uranium despite UN resolutions demanding that it stop, says it wants nuclear fuel only for legitimate production of electricity so it can export more of its bountiful oil and gas.

But it has raised international concern by having concealed activity from the UN nuclear watchdog in the past, continuing to restrict UN inspections and stonewalling an investigation into intelligence allegations of past research into bombmaking.

The EastWest report was the first study of Iran's nuclear and missile potential based on a consensus of US and Russian experts after years of discord between their governments over what to do about Tehran.

Washington has concluded Iran is seeking atomic bombs and poses an immediate threat. The Kremlin says there is no evidence of either. The study's conclusions were presented to top US and Russian foreign policy officials in February.

Former US President George W. Bush conceived the plan for a missile radar and interceptor shield. His successor Barack Obama has said the plan will be pursued pending a review of its costs and technical effectiveness.

The EastWest Institute study said it would not work.

'Not dependable'

"The proposed addition of European-based components (in Poland and the Czech Republic) to the US national missile defence ... has serious weakness ... and cannot provide a dependable defence for Europe or the US against missiles launched from Iran," the report said.

Any country capable of deploying longer-range ballistic missiles could devise measures to evade the shield. "(It) will face great difficulties discriminating warheads launched from Iran ... from the decoys that might accompany them," it said.

Within 6-8 years, it said, Iran could probably produce a missile able to carry a nuclear warhead 2,000 km (1,200 miles) -- a range that a Europe-based shield covering the Middle East, including Iran's arch-enemy Israel, would supposedly counter.

But it is "difficult to imagine circumstances" in which Iran would attack Europe with nuclear missiles since Tehran would suffer a catastrophic retaliatory strike, the report said.

Therefore, an Iranian threat to Europe was not imminent -- "probably not in the next decade" -- and it made no sense to proceed with deployment of the missile shield.

The missile umbrella scheme is fiercely opposed by Moscow, which has called it a threat to its own security, and has figured in renewed US-Russian tensions that have hobbled joint efforts by major powers to curb Iran's nuclear ambitions.

"The urgent task, therefore, is for Russia and the US, and other states, to work closely together to seek by diplomatic and political means a resolution of the crisis surrounding the Iranian nuclear programme," the report said.

"Such cooperation could be helped if the issue of European missile defence were set aside."

Iran on Wednesday test-launched a missile with a range of close to 2,000 km (1,250 miles), official media said, and President Mahmoud Ahmadinejad said Iran could send any aggressor "to hell".

Israel, the Middle East's only nuclear power, fears attack by a nuclear-armed Iran and has suggested it is considering pre-emptive military action, while fretting about Obama's plans to engage Iran dipl