Juergen Stark resigned from the European Central Bank's Executive Board after protesting the bank's bond purchases on a conference call earlier this week, said a euro-area central bank official familiar with the meeting.

During the Sept. 4 call, Stark, 63, expressed his strong opposition to the program, which was expanded last month when the ECB started buying Italian and Spanish bonds, said the official, who spoke on condition of anonymity because the discussions are confidential. Stark was supported by the central banks of Austria and the Netherlands, the person said. The resignation of Stark, the ECB's chief economist, is a blow to the bank, the official said, noting he is the second German ECB member after Axel Weber to leave over the bond program.

Stark's resignation, less than two months before President Jean-Claude Trichet's term ends, suggests policy makers are increasingly split over the best way to fight Europe's debt crisis. The ECB's bond purchases have also been opposed by Bundesbank President Jens Weidmann and his predecessor Weber, who earlier this year pulled out of the running to succeed Trichet.