A Moscow-based activist for Russian opposition party Yabloko has been left blinded after being attacked with an "unknown chemical."

Natalia Fyodorova was hospitalized after an assailant threw the chemical into her face, Yabloko leader Sergey Mitrokhin reported on Twitter.

He said that Fyodorova had lost her sight as the result of the attack, but that it was still unclear if the damage would be permanent.

Fyodorova has been an active campaigner in her local community, focusing on so-called "infill" construction in Moscow. The controversial practice sees developers choose to place high-density, high-rise buildings in otherwise low-lying neighborhoods , ofter overloading local infrastructure.

Mitrokhin said that she had previously faced threats, including incidents when her apartment windows had been shot and a prop casket was delivered to her doorstep.