BERLIN -- German President Horst Köhler threw his country into political confusion Monday by resigning unexpectedly, saying criticisms of his views on German military deployments abroad had shown a lack of respect for his office.

The resignation baffled German government officials because there was no sign of pressure on Mr. Köhler to resign. Chancellor Angela Merkel's governing coalition and left-leaning opposition parties now have 30 days to elect a new federal president, a largely ceremonial role in Germany but one that...