Tehran stands to gain billions of dollars from a 60-day reprieve from US 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 US deal with Iran can translate into lasting economic relief, given the complexity of dismantling a sanctions regime that spans US law, international measures and private-sector risk concerns. The United Nations, the US and the European Union have imposed sanctions and trade embargoes and have frozen assets since the late 1970s over Iran’s nuclear programme, human rights violations and support for militant groups around the region.