By Andrea Shalal and Timothy GardnerWASHINGTON, June 23 (Reuters) - Tehran stands to gain billions of dollars from a 60-day reprieve from U.S. sanctions announced on Monday, but unwinding more than four decades of restrictions poses legal, political and commercial challenges that could take years.At issue is whether an interim U.S. deal with Iran can translate into lasting economic relief, given the complexity of dismantling a sanctions regime that spans U.S. law, international measures and private-sector risk concerns.

The first round of US-Iran negotiations concludes with a temporary lifting of sanctions but progress on the nuclear issue muddied by both sides

The U.S. temporarily removed oil sanctions on Iran Monday, creating the potential for an Iranian economic windfall in U.S. dollars as the first round of talks ended in…