'Constructive' Iran-US talks in Oman draw regional optimism
Discussions welcomed by Saudi Arabia and Iraq, while White House says negotiations were 'very positive'
US architects of original Iran nuclear deal say changed world weighs on talks
Deep mistrust is only one of several obstacles facing the teams heading into the talks in Oman
How Iraq seeks to balance US and Iran ties
Tehran's regional influence has weakened but it is aiming to keep a grip over Baghdad as it enters talks with Washington