Geneva__ Western and Iranian diplomats hailed a new pace, candor and mutual will to try to forge a process to resolve international concerns about Iran's nuclear program, but acknowledged they were at the beginning of a still complex and difficult negotiation whose success is not guaranteed.

"The good news, we are getting to a place where one can imagine we could possibly have a process that could lead to an agreement," a senior US administration official, speaking not for attribution, told journalists Wednesday at the end of two days of nuclear negotiations here, the first since the June election of Iranian President Hassan Rouhani.

"I have never had such intense, detailed, straight-forward, candid conversations with the Iran delegation before," the American official said. "The discussions took place in English...the pace of discussions was much better. It creates the ability to have a back and forth."

"There are [still] serious differences." the US official said. We "got more today than we have ever gotten before, but there's still a whole lot more we have to get."