Iran will receive US investments valued at billions of dollars during the coming phase, said a report by the BBC Sunday.
Iran "has opened a new chapter" in its ties with the world, President Hassan Rouhani said, hours after international nuclear sanctions were lifted, it added.
The US Treasury Department said on Sunday that Washington will allow US companies to deal with Iran through their international branches within the framework of easing sanctions on the country.
The move came after the international nuclear watchdog, the IAEA, said Iran had complied with a deal designed to prevent it developing nuclear weapons.
Most Western governments hailed the move but Israel accused Tehran of still seeking to build a nuclear bomb.
Four US prisoners freed by Iran on Saturday have now left the country.
Washington Post reporter Jason Rezaian, arrested in 2014 and jailed in November for espionage, left on a plane along with three other Iranian-American prisoners as part of a swap with Washington, the paper said.