BRUSSELS--The European Commission said Monday it expects the Spanish government to make a formal request for aid shortly, after euro-zone finance ministers agreed to grant up to EUR100 billion ($125 billion) to prop up the country's financial sector over the weekend.

"We expect Spanish authorities to present a formal request for this assistance shortly," said commission spokesman Amadeu Altafaj Tardio, without adding details.

Speaking during a scheduled press briefing, Mr. Altafaj said the banks needing financial assistance would be "identified in next few days and weeks". He added that many of the details of the rescue plan still need to be worked out, including the conditions that would be imposed on Madrid in return for the rescue. It was also "too early" to say what interest rates would be set on the loan, Mr. Altafaj said.

The commission re-iterated that the International Monetary Fund would "not contribute to the program, but will give its expertise", in a move that breaks with earlier bailout deals agreed for Greece, Ireland and Portugal. "It was decided it was smart and useful to benefit from expertise of IMF even if the fund would not provide financial assistance as such," Mr. Altafaj said.

Write to Vanessa Mock at vanessa.mock@dowjones.com