ATHENS/BERLIN (Reuters) - Germany called yesterday for a financial rescue to be ready for Greece by a May 19 debt deadline after uncertainty over the terms and implementation of the aid package pushed Athens' borrowing costs up to a 12-year high.

Greece's efforts to reassure investors that aid would arrive in time to avert the euro zone's first sovereign debt default proved unconvincing, and there were signs a 45 billion euro ($60.49 billion) EU-IMF aid package would have to be bigger.

The premium investors demand to buy Greek government bonds rather than euro zone benchmark Bunds hit a 12-year high, Greek bank stocks dropped and the euro fell

"The market wants to see the cash laying on the table, not in a coffer beside the table," said David Schnautz, strategist at Commerzbank in Frankfurt.

German Finance Minister Wolfgang Schaeuble sought to ease investors' concerns by saying Berlin aimed to free up financial support for Greece before May 19, when Athens has to refinance an 8.5 billion euro bond.

"I reported Greece's needs to the parliamentary leaders and requested that we arrange the parliamentary debate and decision process so that we are in a position — like the others — to make the necessary loans available to Greece before May 19, if needed," he said.

Germany may be able to finalise a law granting Greece financial aid on May 7, and cautioned that any failure by Athens to refinance the euro bond on May 19 would have unforeseeable consequences, Schaeuble added.

The backing of Germany, Europe's biggest economy, is vital for any aid but Berlin faces public opposition to a financial rescue and is taking a tough line over the terms.

In a possible complication, Germany's opposition Social Democrats said they would not back an accelerated parliamentary process to approve aid for Greece.

Saddled with huge debt and a swollen deficit, Greece bowed to pressure from markets on Friday and formally requested aid, triggering what could be the first financial rescue of a member of the 11-year-old currency bloc.

Athens is in talks with the EU and IMF on additional steps to get the aid flowing in time to meet the May 19 debt deadline.

Athens has already announced billions of euros in budget cuts, including tax hikes and reductions in public sector wages, setting off violent protests and strikes.