Just days after US President Donald Trump called for further isolation of Iran, a Norwegian solar company signed a deal to invest 2.5 billion euros in the country over the next five years.

"Norway is fully committed to the JCPOA (nuclear deal) and this is proof that we have taken the opening very seriously, and we will see more investment very soon," Norwegian ambassador Lars Nordrum told AFP.

He was hosting the signing at his residence in Tehran between Norway's Saga Energy, which will work with Iran's Amin Energy Developers to install two gigawatts of solar panels in multiple sites around the central desert region.

It comes just days after Trump gave a bellicose speech, imposing further sanctions on Iran and calling for European allies to curb their financial dealings with the country.

The new solar project is being financed by a consortium of European private and state investors, and backed by a sovereign guarantee from the government of Iran.

"We hope to build a factory in Iran to build the panels so that we are also generating jobs," said Saga's development manager Gaute Steinkopf at the signing.

"I'd like to thank Norway, which has always been one of the best friends to Iran, for this exciting opportunity," said Saeid Zakeri, head of international affairs for Amin.