WASHINGTON, March 18 (Reuters) - A majority of U.S. senators on Tuesday urged President Barack Obama to insist a final agreement on Iran's nuclear program contains a measure to prevent Tehran from ever having a path to nuclear weapons, as talks on the deal resumed in Vienna.
"We believe any agreement must dismantle Iran's nuclear weapons program and prevent it from ever having a uranium or plutonium path to a nuclear bomb," 83 senators wrote in a letter to Obama on Tuesday. The initiative was spearheaded by Robert Menendez, a New Jersey Democrat and the chairman of the foreign relations committee, and Lindsey Graham, a South Carolina Republican.
Western powers fear that Iran's Arak planned research reactor, once operational, could provide a supply of plutonium, one of two materials including highly enriched uranium that can trigger a nuclear explosion.
How to deal with Arak is one of the thorny issues expected to be tackled this week in the talks between Iran and six global powers over the nuclear program. The talks aim to work out a final deal in the decade-old nuclear dispute by late July.
The U.S. Congress has long taken a harder line on Iran than the White House. Menendez has sponsored a bill to impose new sanctions on Iran, which Obama has threatened to veto if passed. It is stalled in the Senate.
Iran has no inherent right to enrich uranium under the Non-Proliferation Treaty, the senators said in the letter. That is another sticky issue that could complicate the talks.
Iran insists it has the right to enrich low-level uranium for nuclear power plants.
The senators also said Iran must not be allowed to circumvent sanctions during the six-month temporary deal implemented on January 20.
Under that deal, which can be renewed, Iran agreed to curb its nuclear program in return for gaining access to more than $4 billion in oil revenues that had been frozen by Western sanctions.
Backers of strong sanctions have complained that data showing Iran's oil exports increased in February reveals the temporary deal is allowing Iran to get more economic relief than originally thought.
The Obama administration believes that Iran's oil shipments will fall in coming months and will be held to 1 million barrels per day on average from February to July.
But the senators are not convinced. The months during talks on a final deal are "fraught with the danger of companies and countries looking to improve their commercial position in Tehran," the senators wrote.
(Reporting by Timothy Gardner; Editing by Stephen Powell)