By Foo Yun Chee and Sudip Kar-Gupta

BRUSSELS (Reuters) -Deutsche Boerse's European Energy Exchange (EEX) has to seek EU antitrust approval for its acquisition of Nasdaq's European power trading and clearing business because of its importance to Europe's energy market, EU antitrust regulators said on Monday.

The European Commission, which acts as the competition enforcer for the 27-country European Union, said it had been asked by Denmark, Finland, Sweden and Norway to examine the deal even though the acquisition falls below the EU merger rules on turnover.

Under the deal announced in June, Nasdaq will transfer existing open positions in its Nordic, French and German power futures as well as in European carbon emission allowance futures (EUAs) to EEX's European Commodity Clearing (ECC).

EEX is Europe's leading electricity and natural gas exchange, serving 800 participants.

The Commission said the two companies are the only providers of services facilitating the on-exchange trading and subsequent clearing of Nordic power contracts.

"Such services allow for the use of long-term energy contracts with set future prices and are therefore key for more stable and predictable energy prices, to the ultimate benefit of consumers and businesses," it said in a statement.

"It is therefore important to ensure a strong and competitive trading and clearing ecosystem to support the smooth functioning of energy markets, especially in the current context of energy crisis."

This is the third time that the EU antitrust watchdog has used its power under the so-called Article 22 whereby EU countries can request that it reviews deals which do not meet the merger criteria but can impact their markets.

(Reporting by Foo Yun Chee and Sudip Kar-Gupta; Editing by Kirsten Donovan)