Keros Therapeutics' (KROS) largest stockholder ADAR1 Capital Management said Thursday it would like to "work collaboratively" with the board on strategy, capital allocation and potential board changes to unlock value for all shareholders.

In an open letter, the shareholder, which holds around 13.3% of Keros' outstanding shares, said it was disappointed that the company's board refused to engage with it directly. ADAR1 also said it is seeking to meet with the company's independent directors as soon as possible.

The investment manager urged the Keros board to provide a "clear and detailed plan" regarding the planned return of $375 million in excess capital announced on June 9.

Although its preference is a collaboration with the board, ADAR1 said it would seek to elect new directors at the company's next annual meeting if the board continued to refuse its invitations to engage.

Keros did not immediately reply to a request for comment from MT Newswires.

Keros shares were down 1.5% in recent premarket activity.