European banks, which need to refinance more than $1 trillion of debt next year, may struggle to fund themselves until policy makers follow through on a pledge to guarantee their bond sales.

European Union leaders promised this week to "urgently" look at ways to guarantee bank debt in a bid to thaw funding markets frozen by the sovereign debt crisis. Lenders have found it hard to sell bonds for the past two years and have increasingly turned to the European Central Bank for unlimited short-term emergency financing.

"The biggest problem at the moment is that banks haven't been able to fund themselves," said David Moss, who helps manage about 8.5 billion euros ($12 billion) at F&C Asset Management Plc in London. "If banks can't fund themselves, they'll struggle to exist."