(Reuters) - Bitcoin miner Riot Platforms said on Tuesday it had increased its stake in rival Bitfarms to 18.9%.

Riot acquired 1 million common shares of Bitfarms on Tuesday, representing about 0.22% of issued and outstanding Bitfarms common stock.

The acquisition takes the total count of Bitfarms shares owned by Riot to about 85.3 million.

Bitfarms said earlier in the day its co-founder and chair Nicolas Bonta, one of the three board members top shareholder Riot sought to replace, would leave the company immediately.

The two companies have been locked in a dispute since April, when Riot made an unsolicited $950-million offer to acquire Canada-based Bitfarms.

Bitfarms said the bid undervalued it significantly and adopted a "poison pill" to fend off any attempt at a hostile takeover. A poison pill refers to shareholder rights plans used by corporate boards to thwart hostile takeover bids.

Riot withdrew its offer at the time, but is now seeking three seats on the Bitfarms board and has said it is "ready to engage" with the reconstituted board on a potential transaction.