The official commented, on Sunday, as U.S. Secretary of State John Kerry held a series of talks with chief Iranian negotiators and some of the world powers involved in the talks in Vienna.

　　The administration official also said the United States was not troubled by Iranian Foreign Minister Mohamad Javad Zarif's decision to briefly return to Tehran for consultations with his government before the deadline that is two days away.

　　The official said it was expected participants in the talks would come and go from Vienna during the negotiations.

　　Iran Nuclear Talks Likely to Go Past Deadline

　　In a VOA interview, Marie Harf, the State Department Senior Advisor for Strategic Communications, also said negotiators would likely take some additional days after June 30.

　　“We are not looking at a long-term extension of any kind but if we need a few extra days, which it looks like we may, we will take those to get the strongest deal possible,” said Harf.

　　Negotiators have been tight-lipped about the details of the talks but the main sticking points have included the timing of sanctions relief for Iran and the extent of access nuclear inspectors would have to Iranian sites.

　　Several officials have indicated the tough issues remain unresolved.

　　British Foreign Minister Philip Hammond says major challenges remain.

　　Earlier in the day, EU High Representative Federica Mogherini told reporters in Vienna the talks had “always been tough,” but that negotiators could reach an agreement if there is “strong political will.”

　　She also said negotiators had some flexibility, when it comes to time.

　　Conditions remaining

　　On Saturday, French Foreign Minister Laurent Fabius said three conditions still needed to be worked out to ensure a successful agreement.

　　He said those conditions were Iran's acceptance of rigorous inspections of suspected nuclear sites, lasting limits on the country's research and development capacity and a mechanism to quickly re-impose sanctions on Iran if the country violates terms of an agreement.

　　Negotiators have been trying to work through differences over the type and level of access that International Atomic Energy Agency inspectors would have to Iranian sites, including those with possible military dimensions.

　　In April, Iran and the United States, Russia, China, France, Britain and Germany agreed on a plan that was supposed to set the foundation for a final agreement that provided Iran sanctions relief while restricting Tehran's ability to make nuclear weapons.  But some negotiators have indicated there have been disagreements over the parameters set in April.

　　Some diplomats say the real deadline for an agreement is not June 30, but July 9.  After that day, a mandatory congressional review period would extend from 30 to 60 days.

　　It would make sense for negotiators to work past June 30, if need be, to resolve outstanding issues, said analyst Emanuele Ottolenghi of the Foundation for the Defense of Democracies.

　　"It certainly makes sense if the pressure to meet the deadline is going to sort of bring the quality of the agreement into question," he said.  But he said previous extensions in the Iran nuclear talks had resulted in more concessions in favor of the Iranian side.