Back pains suffered by Zarif, Iran's foreign minister and chief negotiator, threatened to complicate the talks. However, Mann said the pains did not stop Zarif from having a "cordial" dinner Monday evening with Catherine Ashton, the top EU diplomat convening the talks.
Araghchi said Zarif was "suffering a lot," although he intended to stay in Geneva until the talks ended. He was later seen leaving the service entrance of his upscale hotel in a wheelchair, with security guards wheeling him into a van.
No final deal is expected at the two-day session, but it potentially could be the launching pad for a deal that has proven elusive since negotiations began in 2003, while reducing the specter of armed conflict in the Mideast.
Israeli Prime Minister Benjamin Netanyahu claims that Iran's new leadership is trying to use the negotiations to trick the world into easing sanctions without making any significant concessions. Netanyahu says a nuclear-armed Iran is unacceptable and has repeatedly threatened to attack Iran, unilaterally if necessary, if diplomacy fails to curb the nuclear program.
Netanyahu appeared to make a new threat against Iran on Tuesday when, during a memorial service marking the 40th anniversary of the 1973 Arab-Israeli war, he said a lesson of that conflict is that "pre-emptive strikes must not be ruled out."
One immediate change from previous talks was the choice of language. Tuesday's sessions were held in English, unlike previous rounds under Mahmoud Ahmadinejad, Rouhani's hard-line predecessor, when English and Farsi were spoken and translations provided of the exchange.
Associated Press Writer Deb Riechmann in Washington contributed to this report.
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