Japan said today it would pledge $60 billion to the International Monetary Fund.
It said it was a critical part of the organisation's bid to boost a global firewall against Europe's debt crisis.
Finance Minister Jun Azumi said he hoped the move would spur other nations to kick in funds.
He said these were "crucial not only to the euro zone but also to Asia and Japan if we are to ensure that the crisis is completely over."
The news comes several days before a Group of 20 finance chiefs' meeting in Washington that is expected to focus on Europe's debt, with the spotlight now on Spain as its borrowing costs spike.
Azumi said today that the $60 billion, which will come in the form of emergency loans using Japan's foreign-exchange reserves, was "important to make public our attitude if we are to help forge an early agreement".
IMF chief Christine Lagarde welcomed the pledge and urged other member states to follow suit. "This is an important step forward to prevent and fight crises and to promote global economic stability," she said.
The Washington-based fund earlier this year said it would likely need an additional $500 billion to help European countries strengthen their defences against the crisis. But Lagarde was quoted in an Italian newspaper report today as saying the lender was scaling back its debt-crisis funding needs to about $400 billion.
Today's effort makes Japan the first non-euro zone country to announce a pledge, which will be formally announced at the G20 talks starting on Friday, and was expected to be among the largest contribution by an IMF member.
Euro zone contributions have so far hit $200 billion, with Beijing and others also expected to kick in as part of the global effort.
Lagarde added that "Japan has a longstanding record of helping others, and of supporting the IMF in its core mission of helping to support economic stability in all its member countries."
Last month, euro zone finance ministers agreed to increase their bail-out funds to €700 billion ($917 billion) from €500 billion, a move that was welcomed by Tokyo at the time.
Europe's debt crisis has come sharply into focus again as dealers grow concerned Madrid will have trouble closing its huge public deficit after an austerity budget that included swingeing cuts to services. Yields on Spain's benchmark 10-year bonds jumped above 6% for the first time since late last year, stoking fears it could follow Greece, Ireland and Portugal in needing a bail-out.
While Azumi said Europe has not done enough to tackle its financial crisis, he has previously praised the European Central Bank for its moves to tackle the simmering issue.
Japan's move comes as a strong yen and sinking demand in key European markets dented its export-oriented economy, with Tokyo a regular buyer of debt issued by the European Financial Stability Facility bailout fund since last year.
The ECB has cut euro zone borrowing costs to an all-time low of 1% and embarked on a hotly contested programme of buying up the bonds of debt-mired countries. In two long-term refinancing operations in December and February, it pumped more than €1 trillion into the banking system in a bid to avert a credit squeeze in the 17 countries that share the euro.
