U.S. Secretary of State John Kerry would arrive in Vienna on Saturday to join the ongoing nuclear talks, a western official confirmed on Friday.
According to the official, Kerry is traveling to Vienna for consultations with European Union foreign policy chief Catherine Ashton and representatives from other P5+1 states (the five permanent members of the United Nations Security Council plus Germany).
The U.S. top diplomat is supposed to "gauge" the extent of Iran's willingness to commit to credible and verifiable steps that will back up its public statements about the peaceful nature of its nuclear program, according to the official.
It has been reported that French Foreign Minister Laurent Fabius would arrive in the capital of Austria on Sunday for the talks.
Kerry might hold bilateral meeting with German Foreign Minister Frank-Walter Steinmeier, discussing the ongoing nuclear talks and bilateral issues, according to the official.
Steinmeier said Friday he would discuss the transatlantic spy row with Kerry when both attend Iran nuclear talks in Vienna this weekend.
Germany's decision to expel the American diplomat is believed to be "unprecedented" in its bilateral relationship. But there are no comments yet from Washington after the expulsion order.
The source said that progress has been made in some key issues in the nuclear talks while big gaps remain regarding Iran's uranium enrichment issue.
Iran and P5+1 group reached a landmark interim deal in Geneva November last year, under which Iran would suspend some sensitive nuclear activities in exchange for limited sanction relief in six months duration, buying time for diplomatic work to find a comprehensive solution for the issue.
Powers demand Iran significantly scale back its nuclear program to address the world concern of its nuclear program, while Tehran insists its nuclear right is inalienable.
Western states have long suspected the real intention of Iran's atomic plan, saying Iran might covertly develop nuclear weapon, an allegation Tehran denies.