U.S. asked Iran to freeze uranium enrichment for 20 years, sources say

The U.S. proposed that Iran accept a 20-year moratorium on uranium enrichment during negotiations in Islamabad over the weekend, according the a U.S. official and a source with knowledge.The Iranians countered with a shorter "single digit" period, according to the sources.Why it matters: The differences over Iran's nuclear program — and in particular, whether Tehran will agree not to enrich uranium and to give up its existing stockpile — were the main sticking point that prevented a deal, the so...