QVT Financial, the US hedge fund, has been joined in its fight to force UniCredit to pay more for its takeover of a Kazakhstan bank by Artradis, one of Singapore's biggest hedge funds.

QVT has accused Italy's UniCredit of abusing minority investors' rights over its attempt to buy preference shares in ATF, the Kazakh bank it agreed to purchase last June for at least $2.2bn. The deal was the first big investment in central Asia by a major western financial services group.