UPDATE 2-Commerzbank ups Bank Forum stake to near 90 pct

* Commerzbank ups Bank Forum stake from 63 pct to 89.3 pct

* Commerzbank buys 26.25 pct stake held by Leonid Yurushev

* Second deal in eastern Europe within days

* Commerzbank shares up 1.4 percent, Forum up 4.9 pct

(Adds detail, background, share price)

FRANKFURT, March 4 (Reuters) - Commerzbank (CBKG.DE) Germany's second-biggest lender, raised its stake in Bank Forum FORM.PFT to almost 90 percent, paving the way for a potential capital increase at the Ukrainian lender.

The transaction comes just days after Commerzbank participated in a capital increase at Polish unit BRE Bank BREP.WA and amid signs that writedowns on bad debt are still on the rise in eastern Europe.[ID:nLDE622159]

Commerzbank on Thursday said it had bought a 26.25 percent stake in Bank Forum but declined to disclose financial details.

The stake in Bank Forum, which was formerly owned by Leonid Yurushev, was bought as part of an asset swap, a person familiar with the transaction said.

The deal raises Commerzbank's stake above the 75 percent threshold needed to push through a capital increase.

Commerzbank said Yurushev had left the group of shareholders in Bank Forum.

At a Bank Forum extraordinary meeting in 2009, shareholders discussed a capital increase and ways to bolster the bank's capital position. Bank Forum made a loss in 2008. The bank has not yet published 2009 earnings.

Bank Forum, in which Commerzbank has held a stake of just over 60 percent since March 2008, has been burdened by its exposure to the struggling Ukrainian economy.

The International Monetary Fund has called on Western banks to help solve a debt crisis in eastern Europe. [ID:nLF947126]

Commerzbank has said it aims to make a profit from its eastern European operations by 2011 after seeing investments sour after an aggressive expansion into the region.

Commerzbank shares were trading 1.4 percent higher at 5.66 euros by 1138 GMT, while the Stoxx European banking index .SX7P was trading 0.9 percent higher. Bank Forum shares gained 4.9 percent.

BRE Bank said this week it would issue up to 20.78 million new shares and Commerzbank, its largest shareholder with a 70 percent holding, would buy its share of the rights. [ID:nLDE6200DD] (Reporting by Edward Taylor and Patricia Uhlig in Frankfurt and Boris Groendahl in Vienna; editing by Elaine Hardcastle)