OSLO (Reuters) -Equinor on Wednesday said it believes the decision of U.S. President Donald Trump's administration to halt the construction of a multi-billion dollar offshore wind power project is unlawful and that the group may take legal action.

In a blow to the nascent U.S. offshore wind industry, Interior Secretary Doug Burgum said on April 16 the Biden administration had failed to conduct enough environmental analysis before approving the Empire Wind development in New York state.

Equinor on Wednesday said the project was about 30% complete at the time it was halted.

The group has spent some $2.5 billion so far, with further exposure including guarantees and termination fees of $1.5 billion-$2.0 billion before taking into account tax and other potential reductions and limitations, it said.

Burgum's announcement this month sent shockwaves through the industry, raising concerns that fully permitted developments are not safe.

"We have invested in Empire Wind after obtaining all necessary approvals, and the order to halt work now is unprecedented and in our view unlawful," Equinor CEO Anders Opedal said in a statement.

"This is a question of the rights and obligations granted under legally issued permits, and security of investments based on valid approvals," he added.

Equinor, majority-owned by the Norwegian state, won a federal lease for the project's site off the Atlantic coast under Trump's previous administration in 2017.

However, on the first day of his second term, Trump ordered a review of offshore wind permitting and leasing, though the fully permitted projects had been seen by analysts as safe.

One of the world's top offshore wind developers, Germany's RWE, last week said it had stopped work on its U.S. projects for the time being in light of moves against the industry by the Trump administration.

Equinor is now seeking to engage directly with the U.S. administration to clarify the matter and is considering its legal options, the company said.

With a planned installed capacity of 810 megawatts, the project could generate enough electricity to power 500,000 homes a year and was expected to begin operating in 2027.

Equinor on Wednesday reported a stronger-than-expected rise in its first-quarter operating profit, boosted by a jump in European gas prices.