Tesla Inc said on Monday the fair market value of the electric-vehicle maker's bitcoin holdings as of December 31 was $1.99 billion.

In its annual filing with the US Securities and Exchange Commission, Tesla, which had invested $1.50bn in bitcoin last year, said it registered about $101 million in impairment losses last year due to the value of bitcoin.

A drop in the value of bitcoin resulted in the company recording losses, as the value of its holdings fell.

Tesla had also briefly accepted the cryptocurrency as payment for sales of certain products.

However, Tesla Chief Executive Officer Elon Musk stopped accepting the digital currency, citing environmental concerns around the mining of bitcoin.

The company said it gained $128 million on sales of bitcoin after selling a portion of its holdings in March. Tesla has not disclosed any change to its bitcoin holdings since.