Spain's public debt rose to 100.5 percent in the first quarter, the central bank said Wednesday as Madrid faces the threat of sanctions from the European Commission for public overspending.

Debt as a proportion of economic output rose from 99.2 percent at the end of 2015, the bank said. It had already surpassed the 100-percent mark for the first time in 20 years in the first quarter of 2015, when it hit 100.2 percent.