Clare Nuttall in Almaty -

In what is the largest claim every made in a UK commercial court case, BTA Bank has filed a new $1.2bn claim against its former chairman, Mukhtar Ablyazov, in the British High Court, according to sources in Kazakhstan.

The lawsuit filed January 21 is the largest of the six claims brought by the bank against the Kazakh oligarch, and brings the total being claimed up to $3.3bn.

Kazakh government officials claim Ablyazov and his associates embezzled around $10bn from BTA, which was nationalised in February 2009. "This is a milestone moment. The claim against Ablyazov is one of the biggest, if not the biggest, being pursued through the commercial court at the moment," a source close to BTA tells bne. "It is interesting from the point of view of BTA's asset recovery, since it almost doubles the amount being claimed. If successful, the benefits for creditors will be substantial."

One of the country's top three banks, BTA veered close to bankruptcy in early 2009 as the financial crisis swept the world, and the Kazakh government had to step in to prevent its collapse. A debt restructuring deal has since been agreed with creditors.

Ablyazov, who fled Kazakhstan in March 2009, says the accusations against him are politically motivated, and continues to maintain that he is innocent of the charges. He has applied for asylum in the UK. But on January 27, the Kazakh General Prosecutor's Office announced it had filed an extradition request for Ablyazov so that he can stand trial in Kazakhstan. The British authorities have not yet replied to the request.

Meanwhile, Kazakhstan's state holding company Samruk-Kazyna is looking for a buyer for BTA, and hopes to sell the bank by the end of this year. Samruk-Kazyna CEO Kairat Kelimbetov said on February 1 that negotiations with Russia's Sberbank could start in April or May after BTA reports its results for the 2010 financial year.