Looking for His glorious appearing! Titus 2:13

"We have made some progress but on some key issues Iran has not moved, from our perspective, from unworkable and inadequate positions that would not in fact assure us that their program is exclusively peaceful," the U.S. official said.

In view of still wide differences in positions, some diplomats and experts believe the negotiations may need to be extended beyond a self-imposed July 20 deadline for an accord.

However, another senior U.S. official said it was difficult to consider extending the talks between Iran and the United States, France, Russia, China, Britain and Russia without first seeing "significant progress on key issues".

"If (a comprehensive agreement) can't happen by July 20 both the administration and Congress are on the same page, which is that we obviously have to consider all of our options."

"But it would be hard to contemplate things like an extension without seeing significant progress on key issues and that is what we are going to be looking for here over the next few days," the official said, also speaking on condition of anonymity.