Iran faces off with global powers in game of brinkmanship

US Secretary of State John Kerry has remained 

in Vienna with his Iranian counterpart

Vienna (AFP) - In a game of high-stakes diplomatic brinkmanship, global powers were readying Wednesday for a late-night push to reach a deal curbing Tehran's nuclear ambitions and ending a 13-year standoff.

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'Zarif is under a lot of pressure. We'll see in the final analysis if we have hit a wall or not. '
Observers say it is hard to believe that after almost two years of intense and tough negotiations the talks could collapse.