Spain's Iberdrola said on Tuesday its brokers successfully placed 10 percent of wind turbine maker Gamesa at 16.10 euros per share, but traders said the price was at the bottom of the price range.

The surprise placement, sold through Morgan Stanley, represented a 4 percent discount to Gamesa's Monday close of 16.78 euros, and shares in the Basque-based firm fell 6.4 percent to 15.70 euros after a trading suspension was lifted.

Iberdrola sold the stake for 391.7 million euros ($557.5 million), making a capital gain of about 112 million euros.

However according to traders the price was at the bottom of a 16.10-16.45 euro range.

There was only demand at or below 16.10 euros. This was a good business for Iberdrola but not necessarily so great for other investors, a Madrid-based trader said.

Analysts said the sale, which leaves Iberdrola with 14 percent of Gamesa, is probably a move by Spain's biggest power utility to improve its financing.

Its debts stand at 34.2 billion euros and it has already said it will sell 2.5 billion euros of assets this year.

(Reporting by Tracy Rucinski in Madrid and Victoria Howley in London, writing by Ben Harding; Editing by Judy MacInnes)