They said Iran is also making advances in rocket technology and could develop a ballistic missile capable of firing a 1,000-kilogram (2,200-pound) nuclear warhead up to 2,000 kilometers (1,200 miles) in perhaps six to eight years.
The EastWest Institute, a nonpartisan organization which focuses on global challenges, said it brought six U.S. experts and six Russian experts together for the first time to produce a joint threat assessment on Iran's nuclear and missile potential. It said key conclusions were presented in February to U.S. National Security Advisor, Gen. James Jones, and Russian Foreign Minister Sergey Lavrov and Security Council Secretary Nikolai Patrushev.
The experts' consensus report, issued by the institute, notes that Iran denies having a nuclear weapons program but says the government has not provided satisfactory answers to the questions raised about possible military dimensions of the program. "While Iran is continuing to enrich uranium," it said, "it is not clear whether it has taken the decision to produce nuclear weapons."
By February 2009, the report said Iran had produced 1,010 kilograms (2,222 pounds) of low-enriched uranium which would be enough for one bomb if it were converted to highly enriched uranium.
To produce weapons-grade uranium, Iran would have to get rid of UN nuclear inspectors from the International Atomic Energy Agency who control and monitor the low-enriched uranium and the enrichment process, the report said.
"It would then be in the range of one to three years...before a nuclear explosive device could be produced," the report said. It might take another five years to produce a nuclear warhead that could be delivered by existing and future Iranian ballistic missiles.
While Iran could, perhaps in six or eight years, develop a missile with a nuclear warhead and a 2,000-kilometer (1,200 mile) range - double its longest-range missile at present - the report said it's virtually impossible to predict how long it would take the country to produce a modern intercontinental ballistic missile.
Without additional outside technology, the report said it would be at least 10 to 15 years, adding that there is no evidence Iran has decided to build an intercontinental ballistic missile.
The timetables could be accelerated if Iran were to receive substantial outside help, the report said.
The scientists and experts concluded that there is no imminent threat of Iran firing intermediate-range or intercontinental ballistic missiles - and if there was such a threat, the proposed U.S. missile defense system in Europe would not provide a dependable defense against it.
It does not make sense, therefore, to proceed with deployment of the European missile defense system in Poland and the Czech Republic, they said.
Former U.S. President George W. Bush proposed deploying a missile defense radar in the Czech Republic and 10 interceptor missiles in Poland. Russia has strongly objected and President Dmitry Medvedev has warned that Moscow will take retaliatory steps if it is deployed.
The report recommends that deployment of the European missile defense system be suspended, and that Russia and the United States cooperate on ballistic missile defense and work closely together to seek, by diplomatic and political means, a resolution of the crisis surrounding the Iranian nuclear program.
Grigory Chernyavsky, one of the Russian participants who chairs the Committee of Scientists for Global Security and Arms Control, said in a statement that it wasn't easy to produce a report both sides could agree on - but the final result provides a solid technical base for decision-making.