Banco Santander (SAN.MC) is looking to list its Mexican unit in Mexico and New York on September 25, a source close to the deal told Reuters late on Thursday.

The move is part of Santander's bid to shake off its association with its struggling home market, allowing it to remind investors of its international reach and paving the way for a listing of its British subsidiary next year.

The bank is considering listings in other parts of the world following its pattern of offerings for units in Brazil and Chile in recent years, the Mexico-based source said. The source added that he did not have details on the planned British listing.

The euro zone's biggest bank, which has suffered less than domestic rivals from the economic crisis in Spain because of extensive overseas interests, is looking to raise between $3 billion and $4 billion in the offering, Thomson Reuters IFR reported last week.

"It is very premature to talk about the pricing, the ranges are still very wide," the source said. "The date could change, but only if there was something serious in financial markets."

Book runners of the deal have started meetings with fund managers ahead of roadshows, which are expected to start shortly.

The Ve por Mas brokerage in Mexico City said it expects the Mexican portion of the listing to be priced at around 36.40 pesos a share, while other analysts forecast a range of between 30 to 37 pesos.

Santander plans to list about 25 percent of its Mexican unit, which is Mexico's third-largest bank by assets, with just over 6 percent being sold in Mexico and 18.7 percent abroad.

Spain accepted a 100 billion euro ($125.83 billion) European Union rescue to prop up its banks, although Santander is not expected to need any aid. The bank boasts a higher credit rating than the Spanish state, which is now inching towards a full sovereign bailout.

Santander press officers in Madrid were not immediately available for comment on the listing plans.

The bank upset investors this week when it said it would buy back some of its subordinated and hybrid debt, just one day after pricing a senior unsecured issue, ending a six-month debt freeze in the Spanish banking sector.

Santander, which saw first-half profits more than halve after writing down the value of Spanish real estate assets, said it wanted to improve the management of liabilities and strengthen its balance sheet.

MEXICAN PROMISE

Santander said in a preliminary prospectus that it saw Mexico as a good growth prospect due to its sound economic fundamentals, young population, growing middle class and low penetration of banking services.

The bank had 841 billion Mexican pesos ($64.10 billion) in assets and a loan portfolio of 338.9 billion pesos at the end of June.

Although Santander's geographic reach, particularly in Latin America, has shielded it from the worst of the Spanish crisis, revenues have fallen in the region.

Earnings tumbled at Santander Brazil SANBR.UL (SANB4.SA), which accounts for over a quarter of group profit. Slowing economic growth there has resulted in higher credit losses for the bank.

Santander's listing will be the third this year on Mexico's stock exchange, which has in recent years sharply lagged its larger neighbor Brazil in attracting companies looking for capital.

Global IPO proceeds plummeted 46 percent in the first half of this year, as Europe's debt crisis and worries over economic growth from China to the US have left stock markets choppy and unpredictable

While some high profile IPOs such as London luxury jeweler Graff Diamonds' planned Hong Kong float have been canned, others which went ahead, such as that of Facebook (FB.O), have left a bad taste in investors' mouths.

Bankers say only those companies with strong balance sheets, significant growth prospects and stories easy for investors to understand are being advised to risk testing the waters.