VIENNA - Iran and six world powers will try to make headway toward resolving their nuclear dispute in talks starting in Vienna on Tuesday, with Western officials hoping the challenge will not be made even more difficult by the Ukraine crisis.
So far, diplomats say, there is little sign that the worst East-West confrontation since the Cold War will undermine the quest for a deal to end the standoff over Iran's atomic activity and avert the threat of a Middle East war.
But unity among the powers on Iran may be tested in the meeting of their chief negotiators on the issue in the Austrian capital Vienna, with the four Western states and Russia.
One Western envoy said there had been no apparent spillover from the Ukraine situation on expert level talks between Iran and the powers - the United States, France, Germany, Britain, China and Russia - held two weeks ago.
"We hope that will continue to be the case," the diplomat said.
The United States and European Union have imposed sanctions including asset freezes and travel bans on some senior Russian and Ukrainian officials after Crimea applied to join Russia on Monday following a secession referendum.
Russia will be represented at the talks - which are expected to start around 10:30 am (0930 GMT) on Tuesday and are likely to end late on Wednesday - by Deputy Foreign Minister Sergey Ryabkov. European Union foreign policy chief Catherine Ashton will lead the negotiations on behalf of the powers.
Iranian media said Iranian Foreign Minister Mohammad Javad Zarif had cancelled a customary pre-talks dinner with Ashton on Monday evening. The official IRNA news agency quoted sources as saying it was because of Ashton's "undiplomatic" behaviour, an apparent reference to her meeting Iranian human rights activists during her first visit to Tehran 10 days ago.
Despite a concerted push to end the decade-old nuclear dispute after a relative moderate, Hassan Rouhani, was elected president last year on a platform to end Iran's international isolation, big power divisions have reared their head before.