Sadly, I think that the Iranians are stalling, and are making fools out of Kerry and Obama and the West.
Dr Alf is right in this regard, as per some of his earlier posts.
Attacking Natanz can only be done by the Americans, using powerful thermobaric weaponry and that would be regarded as an act of war by Russia. Israel lacks the capability to attack Natanz, so the need is to concentrate the minds of the Ayotollahs without triggering war.
Using weather warfare to decimate Iran’s crops and food supply and create a small earthquake to destroy Natanz might be part of the solution and holding out the possibility of a wealthier secular future under a more Western friendly regime might be the way to stop the present regime’s trouble-making short of going to war.