Czech private equity group Penta Investments and fund Eastbridge sweetened their bid for Polish retailer Empik Media & Fashion (EM&F) for the second time in two weeks on Tuesday, hoping to quash efforts by another investor to derail the bid.

Penta and Eastbridge, which currently owns 60 percent of EM&F, increased their bid to 10.45 zlotys per share from 10.38 zlotys, valuing the latest offer for the remaining 40 percent at 436 million zlotys ($136 million).

The offer launched in mid-March concludes on Tuesday.

Eastbridge Chief Executive Maciej Dyjas said the two bidders were determined for the offer to succeed even though it faced unexpected competition from another market player, which over the last several days had bought an 8 percent stake.

He declined to name the rival, but sources close to the offer said it was pension fund ING OFE.

ING OFE, which at last count had a 6 percent stake in EM&F, declined to comment.

Eastbridge and Penta had previously said they needed to raise their stake to at least 80 percent to allow them to delist EM&F, but on Monday said they could settle for less.

"Delisting will take place sooner or later," Dyjas told Reuters. "We will wait for emotions to subside and it is likely that with time we will buy the remaining shares at a lower price."

EM&F operates about 750 stores in central and eastern Europe and opened Poland's first GAP outlet last year.

Its holdings include Poland's leading chain of toy stores Smyk, as well as book and newspaper retailer Empik. The group has recently been hit by weaker sales in clothes and cosmetics.

Under Polish law, an investor is required to launch a public offer if it buys more than 10 percent of a company within 60 days. A shareholder must also declare its position after surpassing a 10-percent holding.

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