June 10 (Reuters) - Bitcoin miner Bitfarms said on Monday it had approved the adoption of a "poison pill" to fend off a potential hostile takeover attempt by rival Riot Platforms.

The move comes days after Riot Platforms disclosed it had built a 12% stake in Bitfarms as it pursues a takeover attempt. Riot had offered to buy Bitfarms for about $950 million last month.

Bitfarms said the shareholder rights plan aimed to preserve the integrity of its previously announced strategic alternatives review process.

Poison pill plans, including shareholder rights plans, are used by corporate boards to thwart hostile takeover bids.

Under Bitfarm's plan, if an entity accumulates more than 15% of Bitfarms' stake after June 20 and up to Sept. 10, the company would issue fresh shares, diluting the entity's stake.

After Sept. 10, the threshold would be relaxed to 20% as long as any takeover attempt meets certain conditions.

(Reporting by Arasu Kannagi Basil in Bengaluru; Editing by Tasim Zahid)