Explainer-What challenges could stand in the way of a final US-Iran deal?

<p>By Matt Spetalnick</p><p>WASHINGTON, June 17 (Reuters) - When U.S. and Iranian negotiators sit down in Switzerland on Friday after nearly four months of war, the stakes couldn’t be higher as they face an array of hurdles that could derail efforts to reach a comprehensive peace agreement.</p><p>While a breakthrough cannot be ruled out, most analysts are skeptical the two sides can forge a final settlement within the 60-day window laid out in a “memorandum of understanding” that President Donald Trump and Iranian leaders approved this week.</p>