Amber Capital said it had sent a letter on July 18 to Suez's management, outlining its demands, as activist funds such as Elliott and others target companies across Europe.

London-based Amber Capital, which holds 1.9% of the French utility's share capital, called for Suez to reduce the size of its board of directors to between 12 and 14 from 19 at present, and to review its portfolio of assets.

"Suez needs a strategic reset: The new management team of Suez now has a compelling opportunity in our view to reposition the company," Amber Capital said in a statement.

"After years of limited portfolio management, Amber Capital believes the company needs a thorough portfolio review to rotate out of mature assets and use proceeds to reinvest, delever and buy back shares," added Amber Capital.

In response, Suez - in which French utility Engie has a 32% stake - said a strategy review was already underway and would be presented in the autumn.

Amber Capital has also called on French media company Lagardere to do more to boost shareholder value, while Elliott has targeted companies such as drinks group Pernod and tourism and insurance company Saga.

(Reporting by Sudip Kar-Gupta, Editing by Sherry Jacob-Phillips and Jane Merriman)

By Sudip Kar-Gupta and Geert De Clercq