US official: Next round of Iran nuclear talks 'pretty tough'
Among key issues yet to be resolved are the sequencing of sanctions relief for Iran and establishment of monitoring and verification measures to ensure that agreement will not be violated.
Iran's FM Zarif (C on left) and head of the AEO of Iran Salehi (C on right) with colleagues in Lausanne March 19, 2015 (photo credit: REUTERS)ByREUTERS
