Aug. 8 (Bloomberg) — European Central Bank President Mario Draghi's bid to bring down Spanish and Italian yields may spur the nations to sell more short-dated notes, swelling the debt pile that needs refinancing in the coming years.

Yields on Italian and Spanish two-year notes plunged after Draghi said on Aug. 2 the ECB may buy debt on the "short-end of the yield curve" as part of a broader crisis-fighting plan. The gap between Spain's two-year and 10-year yields rose on Aug. 6 to the widest in at least two decades, while the spread between similar Italian securities also approached a record.

The average maturity of Spanish debt is the shortest since 2004 as Spain, like Italy, hasn't issued 15- or 30-year bonds all year. As Prime Ministers Mario Monti and Mariano Rajoy fight to avoid bailouts that may threaten the euro's survival, the ECB's plan risks adding to pressure on the two nations' treasuries.