Gas Natural could face a battle for Endesa

The $28.2bn (�15.3bn; 22.6bn euro) offer is Europe's biggest attempted takeover this year and would create the world's third-largest utility.

Previous attempts to combine Spanish energy firms were unsuccessful.

Endesa called off a merger with rival Iberdrola in 2001, while Iberdrola defeated a bid by Gas Natural in 2003.

"The board of Gas Natural today approved unanimously the launch of a takeover bid for the purchase of 100% of the capital of Endesa," the group said in a statement.

Gas Natural said the cash and shares offer was worth 21.3 euros a share, 12% higher than Endesa's closing price on Monday.

It said shareholders taking up the offer would receive 7.34 euros and 0.569 new shares in Gas Natural for each Endesa share held.

Just before the announcement, an Endesa spokesman told the AFP news agency that any bid by Gas Natural would be met with a "full-on rejection".