PARIS (Reuters) -U.S. Treasury Secretary Janet Yellen said on Thursday the World Bank should add disaster clauses to debt agreements with poorer countries, speaking ahead of a summit in Paris that will discuss how to boost crisis financing for low-income nations.

Such clauses could be part of a broader reform of the World Bank to free up more funds, Yellen told journalists in the French capital.

"We would also like to see the World Bank offer borrowers the option to add climate resilient debt clauses to their loan agreements. These clauses would help ease pressures on countries if a natural disaster strikes," she said.

Yellen, whose country is the World Bank's biggest shareholder, added multilateral development banks should be reformed to become more efficient before shareholders think of injecting more money into them.

"Even with the capital that the World Bank and the MDBs have there is clearly potential ...to increase financing capacity," she said, adding an additional 200 billion dollars could be unlocked over a decade.

"We are certainly not ruling out at some later stage a capital increase. But I think that these banks need to function better individually and as a system first, expand their mission to address global challenges, better utilize the capital they have."