Iran and world powers are aiming to finish the latest round of nuclear talks "in the timeframe" that all parties have set out, said US Secretary of State John Kerry in Vienna on Sunday."That's our goal," Kerry said, adding that the United States will "put every bit of pressure possible on it to try to do so".

After meeting with his Iranian counterpart Mohammad Javad Zarif on Sunday afternoon, Kerry told reporters that "it is now time to see whether or not we are able to close an agreement", with top diplomats returning back to Vienna on Sunday.

However, despite genuine progress made in the past few days, Kerry said: "We are not yet where we need to be on several of the most difficult issues."

Kerry also told reporters that while he completely agrees with Zarif that Iran and world powers "have never been closer" to a deal, the negotiation could go either way at this point.

"We want a good agreement. Only a good agreement. We are not gonna shave anywhere at the margins just to get an agreement," he added.

Zarif said on Friday in a video on YouTube that despite some remaining differences, Iran and its counterparts "have never been closer to a lasting outcome".

Iran and the five UN Security Council permanent members plus Germany (P5+1) missed the previously June 30 deadline for a comprehensive deal. Both sides agreed to extend the deadline to July 7.

In a successful deal, Iran would suspend some sensitive nuclear activities, and in return, Western states would partially relieve some sanctions imposed on Tehran.