Kazakhmys, the copper miner, has effectively blocked its biggest rival Eurasian Natural Resources Corporation from making a hostile bid for it by raising its stake in its corporate compatriot to just over 25 per cent.

Kazakhmys said on Monday it had lifted its stake from 22.2 to 25.02 per cent, a rise that gives it the ability to block any special resolutions ENRC might propose that require a 75 per cent majority.