Spain's distressed banks need about 40 billion euros ($50 billion) in new capital, the IMF has warned, ramping up the pressure for emergency eurozone talks over the weekend on a huge bailout package.
Eurozone finance ministers will hold a conference call at 1400 GMT on Saturday on Spain's expected request for aid to shore up its distressed banking sector, European government sources said.
The eurozone greenlighted the "holding of a teleconference of the Eurogroup on Saturday at 4:00 pm to agree a declaration on Spain's intention to request aid and the Eurogroup's commitment to granting it," a European government source said.
Officials will be able to consider new stress tests carried out by the International Monetary Fund, which showed that while Spain's top two banks -- BBVA and Banco Santander -- remain solid, the rest of the banking sector is struggling.
If the current stress on the system continues "the largest banks would be sufficiently capitalised to withstand further deterioration, while several banks would need to increase capital buffers by about 40 billion euros", the IMF said in a statement on Friday.
If Madrid feels it has no option but to ask for help, it would mean the eurozone sovereign debt crisis has defied the authorities' desperate attempts to limit the need for rescues to Greece, Ireland and Portugal.
It would also see the eurozone in uncharted waters after two years of turmoil -- Spain's economy is the fourth-largest in the eurozone and more than twice the size of Greece's, Ireland's and Portugal's combined.
"The 'Euro working group' is on stand-by, ready to meet this weekend should there be a request from Spain," a source said, amid heightened fears that Spain's problems could cause contagion throughout Europe.
Dutch Finance Minister Jan Kees de Jager said he could not exclude the possibility of a weekend meeting while European Central Bank Vice President Vitor Constancio called Friday for swift action.
"Spanish banks have recapitalisation needs, therefore a solution must be found quickly to calm the markets," Constancio said.
Media reports earlier said Spain could ask for a bank rescue -- estimated by Fitch Ratings at up to 100 billion euros ($125 billion) -- as early as Saturday.
US President Barack Obama on Friday urged Europe to act swiftly to fix its banking woes or pay the price.
"In the short term they have got to stabilise their financial system. Part of that is taking clear action as soon as possible to inject capital into weak banks," he told reporters.
"Just as important, leaders can lay out a framework and a vision for a stronger eurozone, including deeper collaboration on budgets and banking policy," he added.
Obama spoke with French counterpart Francois Hollande by phone on Friday and the pair agreed on the need to stimulate growth in Europe, the French president's office said.
Socialist leader Hollande, who took office last month, made easing austerity measures a centrepiece of his winning election campaign, a line that has ruffled feathers in Germany, which is preaching fiscal responsibility.
Obama and Hollande "agreed to work closely together... to promote growth and financial stability", the French presidential office said in a statement, a sentiment echoed by the White House.
International Monetary Fund Managing Director Christine Lagarde also urged European leaders to act without delay to overcome the crisis, warning that "we stand at a crossroads".
Lagarde appeared to respond to German Chancellor Angela Merkel, who spoke about long-term plans of rebuilding Europe.
"Policymakers need to lay out and follow a clear roadmap of how to finish the job -- not just looking to the next five or 10 years, but looking to the next weeks and months ahead," Lagarde said.
Spanish financial markets, with stocks up nearly two percent Friday, were betting on an imminent bailout restricted to the banking system, a model that would save Spain from the humiliation of a Greek-style rescue with all the painful austerity conditions attached.
Ratings agency Fitch slashed Spain's rating by three notches to BBB from A on Thursday, citing ballooning estimates of the cost of a banking crisis, mushrooming debt and a deepening recession.
A bank rescue would also push up the state debt, Fitch predicted, warning that gross general public debt would likely peak at 95 percent of total economic output in 2015.
A string of top European policymakers refused to confirm plans for a weekend telephone conference call but most said Europe was ready to spring into action the moment that it was required.
"No decisions of any kind have been taken," Spain's Deputy Prime Minister Soraya Saenz de Santamaria told a news conference, stressing that Madrid was waiting for an audit of the banks' balance sheets.
A rescue package might soothe investors by resolving many questions over a banking sector crippled by its massive exposure to a property market that collapsed in 2008.
The Bank of Spain -- which got a new head Friday in the shape of Luis Maria Linde -- said an independent audit of the banking system, examining how much extra capital is needed, would be submitted by June 21.
Linde, 67, replaces Miguel Fernandez Ordonez, who stepped down last month.