Major issues remain unresolved in the Iran nuclear talks, a senior U.S. official said on Sunday in a comment that appeared designed to play down speculation that an agreement was imminent.

"We have never speculated about the timing of anything during these negotiations, and we're certainly not going to start now - especially given the fact that major issues remain to be resolved in these talks," the senior U.S. State Department official said in an emailed comment.

By Reuters