Talk of new US sanctions in recent months has created "a great deal of concern" in Iran on whether Washington is serious about a nuclear deal, Iran's foreign minister said Tuesday.
"Unfortunately what we have seen in the last two months has not encouraged us to believe that everything is in order," said Mohammad Javad Zarif, speaking from Vienna on the first day of nuclear talks.
"I can understand the politics... in the United States... but from the general perspective of the Iranian populace what has happened in the last two months has been less than encouraging," he said.
Certain statements "have created a great deal of concern in Iran on whether the US is serious about wanting to reach an agreement".
He added: "But nevertheless, these statements aside, it is really possible to make an agreement because of a single overriding fact, and that is that we have no other option.
"If we want to resolve this issue the only way is through negotiations," he said, speaking from Vienna in a webcast discussion organised by Denver University's Center for Middle East Studies.
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US President Barack Obama has had to fight hard to stop sceptical members of Congress, including some from his own party, from passing additional sanctions on the Islamic republic.
Such a move would contravene the terms of an interim nuclear deal struck in November by Iran and the five permanent members of the UN Security Council plus Germany under which Tehran scaled back its nuclear activities for six months.
Talks began in Vienna on Tuesday between Iran and the United States, China, Russia, Britain, France and Germany on translating this deal into a lasting accord.
Zarif said that the talks "started on the right track" on Tuesday, saying he hoped to reach a deal before the six-month deadline -- which can be extended -- on July 20.
"We have a shared objective, and that is for Iran to have a nuclear programme that is exclusively peaceful," he said.
He said a deal was "totally achievable" but would take more than "one or two sittings".
"I hope by July we can finalise this deal and move it in the right direction of implementing it," Zarif said, adding that getting an accord will take "some innovation and some forward thinking".
The talks in Vienna were due to resume on Wednesday.