Iranians celebrated in the streets after negotiators reached a framework for a nuclear accord and US President Barack Obama hailed an "historic understanding", but senior global diplomats cautioned that hard work lies ahead to strike a final deal.
The tentative agreement, struck on Thursday after eight days of talks in Switzerland, clears the way for a settlement to allay Western fears that Iran could build an atomic bomb, with economic sanctions on Tehran being lifted in return.
It marks the most significant step towards rapprochement between Washington and Tehran since the 1979 Iranian revolution and could bring an end to decades of Iran's international isolation.
Celebrations erupted in the Iranian capital after the deal was reached. Cars in Tehran honked horns as passengers clapped.
On Friday, conservative clerics signaled their support, including Ayatollah Ali Khamenei, the supreme leader, whose authority exceeds that of the elected president, Rouhani.