Banco Santander SA's (STD) Argentinian unit will use proceeds from its upcoming share sale to expand its branch network, and is actively seeking "material acquisitions in the near to medium term," the bank said Thursday in a prospectus filed with the U.S. Securities and Exchange Commission.

The unit, Banco Santander Rio SA (BRIO.BA), has requested approval from Argentine and U.S. stock market regulators to list new shares.

In the prospectus, Santander Rio said it may open approximately 100 new branches and install 200 new automatic teller machines by 2013, increase its loan portfolio, and to "fund inorganic growth to the extent we are able to complete appropriate acquisitions."

In a separate Spanish regulatory filing, the Spanish banking giant said it hasn't yet decided how many new shares it will sell in the offering.

Santander first announced its intention to sell new shares in its Argentine unit in February as part of its strategy to raise capital through the sale of minority stakes in some of its operations around the world.

It has also said it wants to sell shares in its U.K. unit before the end of this year.

-By Christopher Bjork; Dow Jones Newswires; +34913958123; christopher.bjork@dowjones.com