Spain's Banco Santander said Thursday it planned to register an initial public offering of shares in its Mexican unit "in the next few days" on the New York and Mexico City stock exchanges, with the stock sale expected to take place by the end of the year.

Santander said in a filing with Spanish stock market regulator CNMV that it expected to retain "broad majority" control of the Mexican unit following the IPO.

The bank has not yet determined when the IPO will be executed or what percentage of the Mexican operation will be sold, but CEO Alfredo Saenz said during the banking giant's last presentation of results that the move was likely "in the course of this year," sources at Banco Santander told Efe.

Other sources said Santander might be looking to sell up to 30 percent of its Mexican subsidiary, generating proceeds of some 3.2 billion euros (nearly $4 billion).

The IPO will be structured with tranches being sold simultaneously on the Mexican market and on the international market, Banco Santander said.

The shares will be listed on the Mexico City Stock Exchange and on the New York Stock Exchange, with documents for the IPO being filed in the next few days, the bank said.

Citigroup, JP Morgan Chase, Deutsche Bank and Santander will handle the IPO, other sources said. EFE