...and had not progressed in a major acquisition.
The stock closed at 1,310 crowns ($72.41) by 1437 GMT, dragging the Prague bourse's index PX down 1.43 percent.
The company agreed an alliance with Hungarian MOL on Thursday including the acquisition of a 7 percent stake in the oil group and the building of gas-fired power plants.
Analysts and traders said Thursday's announcement on the MOL deal was widely expected and had been already priced in, but a lack of progress in a bid for a lignite mine and interruption to the share buyback were negative.
"From the set of yesterday's news, the investors were inspired by those that were negative in the short-term," said Vladimir Vavra, trader of KBC's Czech brokerage Patria Finance.
CEZ had bought back 8 percent of its shares by Thursday in a buyback programme of up to 10 percent. It said it would interrupt the buyback until the last week of January.
CEZ also said it was interested in buying Mostecka Uhelna, in northern Czech Republic, which is key for its plans to renew power plants in the region, but had so far reached no agreement on the issue.
(Reporting by Jan Korselt; Editing by Quentin Bryar)
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