MEXICO CITY (Reuters) -Citigroup ( C/PN ) on Thursday rejected Mexican mining and transport conglomerate Grupo Mexico's bid for its retail unit in the country, known as Banamex, opting instead to push forward with a previously agreed-upon deal.

Grupo Mexico surprised last week when it made an unsolicited $9.3 billion offer for Banamex, more than two years after it had backed away from negotiations.

The news rocked local markets, wiping off billions in the firm's market capitalization. Shares in Grupo Mexico climbed more than 4.5% on Citi's statement Thursday that it rejected the bid.

Citi last month announced that it would sell a 25% stake in Banamex to Mexican billionaire Fernando Chico Pardo, chairman of airport operator ASUR, for around $2.3 billion. The lender then planned to hold a public offering for the rest of the unit, it said at the time, while also gauging the interest of other local magnates.

Citi on Thursday said that it believed that deal was the best option to divest from Banamex responsibly and maximize value for shareholders.