Amid a spreading financial crisis, the spokesman, Torsten Albig, said state protection would be extended to all personal savings and checking accounts.
He later told the business daily Handelsblatt that the value of such holdings was estimated to be €568 billion (€784 billion).
"The government wants to prevent at all costs money being withdrawn on a grand scale," he said.
German Chancellor Angela Merkel had made a pledge earlier in a statement to reporters: "We tell all savings account holders that your deposits are safe. The federal government assures it."
The conservative leader made the remarks as she said her government was scrambling to salvage a rescue plan for German bank Hypo Real Estate (HRE) so "an institution's crisis does not become a crisis for the entire system".
Finance Minister Peer Steinbrueck said in a joint statement that German taxpayers need not worry about "a single euro of their deposits" in the crisis.
Meanwhile two of Germany's biggest private banks, Deutsche Bank and Commerzbank, said their liquidity needs were covered through the end of the year.
Private savings is a particularly sensitive issue in Germany which has one of the highest savings rates in the developed world and where memories of the Great Depression and the ensuing rise of the Nazis are still alive.
Interior Minister Wolfgang Schaeuble even invoked that history as he warned of the potential political repercussions that could follow the current world financial crisis.
"We learned from the worldwide economic crisis of the 1920s (and 1930s) that an economic crisis can result in an incredible threat for all of society," he was quoted as saying in an advance copy of Der Spiegel's Monday edition.
"The consequences of that depression was Adolf Hitler and, indirectly, World War II and Auschwitz."
Last year, Germans set aside some 11 percent of their disposable income, mainly for retirement, according to the Association of German Banks.
The blanket protection resembled an emergency law passed by Ireland Friday providing an unlimited guarantee on bank deposits. But the German plan only covers individual savings and checking accounts.
Merkel had sharply criticised Ireland's go-it-alone plan after crisis talks in Paris Saturday with the leaders of France, Britain and Italy.
"We have already asked the European Commission and the European Central Bank to try to talk to Ireland," she said. "It is important to act in a balanced way, and for countries not to cause harm to each other."
German law foresees a 90-percent guarantee for private deposits capped at €20,000euros ($28,000). All savings accounts are normally fully covered by federal deposit insurance.
But the savings deposit insurance fund of the Association of German Banks was hit by heavy losses linked to the bankruptcy of US investment bank Lehman Brothers in September.