Shares of embattled electric-truck start-up Nikola (NKLA -2.22%) closed down more than 25% on Wednesday, following reports that energy giant BP (BP -1.04%) has backed away from a potential partnership following allegations that Nikola has misled investors. 

Nikola's stock fell sharply following a Wall Street Journal report that the company's negotiations with several potential partners, including BP, had stalled after a short-seller's report cast doubt on the truck maker's technology claims. 

The U.S. Securities and Exchange Commission also is investigating the allegations. 

Nikola has been seeking a partner to help it build a network of hydrogen refueling stations, a key component of its business plan for electric heavy trucks powered by hydrogen fuel cells. 

The Nikola One, a white electric semi truck.

Did Nikola mislead investors? The company hasn't denied allegations that its original prototype, the Nikola One semi, didn't propel itself. Image source: Nikola.

Nikola plans to offer the trucks to commercial-fleet operators via a 7 year or 700,000 mile lease, with maintenance and refueling — via a Nikola-owned network of stations — included in the lease cost. 

Nikola and BP had a deal in principle and were just a few days away from an announcement when the short-seller, Hindenburg Research, published its report on Sept. 10, according to a Bloomberg report. 

The deal with BP would have been announced just a few days after Nikola announced a separate deal with General Motors (GM -2.48%), in which the two companies will collaborate on an electric pickup truck. Nikola also agreed to buy battery packs and fuel cells from GM. 

Through Wednesday's close, Nikola's stock had lost about half of its value since the Hindenburg report was published. While GM has said that it stands by its deal with Nikola, the report has already had other ramifications: Nikola's outspoken founder, Trevor Milton, left the company early on Monday and deleted his widely-followed Twitter account.