The London Stock Exchange said on Monday that it was investigating trades in Anglo-Russian precious metals miner Polymetal after the shares surged 700%.
The LSE is looking at trades carried out between 0840 GMT and 0900 GMT. Some of them could be cancelled, it said, adding that a further update will be made in due course.
At 1040 GMT, the shares were up 25.% at 213p, having jumped to as high as 1,400p earlier in the morning.
