Jose Ignacio Goirigolzarri, the bank's president, said late Friday that the bailout would "reinforced the solvency, liquidity and solidity of the bank."
The request came as Standard & Poor's downgraded Bankia and four other Spanish banks to junk status because of uncertainty over restructuring and recapitalization plans.
Trading in Bankia shares was suspended Friday while its board determined how much new aid was needed. The bank's shares have experienced turbulent trading in recent weeks on fears it would not be able to cover the massive losses it has built up in bad loans to the country's collapsed real estate sector.
Concern about the health of Europe's banks is a key constituent of the region's financial crisis. Spanish banks are seen as particularly shaky because they were heavily exposed to the country's collapsed real estate bubble and now hold massive amounts of soured investments, such as defaulted mortgage loans or devalued property. Bankia has been the worst-hit and holds €32 billion ($40 billion) in such toxic assets.
Bankia S.A. was created from the merger of seven regional banks, or cajas, that were deemed too weak to stand alone. But financial concerns continued to plague it — its shares have lost almost half their value since the lender went public last July.
The government decided to intervene earlier this month, effectively nationalizing Bankia, and injected €4.5 billion ($5.7 billion) in aid.
Its shares closed at €1.6 ($2.01) on Thursday after shedding more than 7 per cent.
The Spanish government is trying to shore up the banking sector to get credit flowing to the ailing economy. But the cost of rescuing banks could overwhelm government finances, which are strained by a recession and an unemployment rate of nearly 25 per cent.
The possibility that the Spanish government might eventually need an international rescue package — like the ones Greece, Ireland and Portugal sought — has kept investors on edge for months.
Spanish Prime Minister Mariano Rajoy met with Socialist opposition leader Alfredo Perez Rubalcaba late Friday to try to map out a strategy for the future.
The big fear is that if Greece eventually leaves the euro, confidence in other financially weak countries like Spain and Italy could fall, causing the value of their bonds to drop. Ultimately, the worry is that could undermine confidence in the system and create bank runs.
To avert such a disastrous scenario, financial experts are increasingly calling for a Europe-wide support system for the banks.
"The euro area financial stability framework needs an urgent overhaul," said Peter Praet, one of the European Central Bank's six-member executive committee.
He said there should be a eurozone-wide banking regulator with the money and authority to restructure banks operating across borders as well as a deposit insurance program similar to the U.S. Federal Deposit Insurance Corporation. Both measures would be funded by the private sector, not the government, to not expose taxpayers to more banking crises.
Asked whether Spain would seek outside help for its banks, Deputy Prime Minister Soraya Saenz de Santamaria at a weekly government press conference earlier Friday reiterated the government's position, saying firmly, "Not at all."
The flare-up in the debt crisis in recent months, with a Greek exit from the euro openly discussed, has sent Spain's borrowing costs soaring to levels that Prime Minister Mariano Rajoy said the country could not put up with for very long.
The yield for key 10-year bonds on the secondary market — an indicator of investor wariness — edged up to a perilously high 6.29 per cent by close of trading Friday. A rate of 7 per cent is considered unsustainable over the long term.
Spain's benchmark IBEX35 stock exchange ended Friday trading up 0.13 per cent.
Foreign investors in particular appear to be dumping Spanish government debt. In the first four months of the year the amount they held fell 24 per cent to €213 billion, according to the latest figures released Friday by the Economy Ministry. As of the end of 2011, foreign investors held just over 50 per cent of Spain's debt but by the end of April that figure dropped to 37.3 per cent.
Bankia also announced Friday that it had shaken up its board of directors, reducing it from 18 to 10 members.
Daniel Woolls contributed to this report