Germany's opposition leader vowed Thursday to bar people from entering the country without proper papers and to step up deportations if he is elected chancellor next month, as a knife attack by a rejected asylum-seeker spilled over into an election campaign in which he is the front-runner.

Two people, including a 2-year-old boy, were killed and three injured Wednesday in the Bavarian city of Aschaffenburg. The suspect, arrested shortly afterward, is a 28-year-old Afghan with a history of psychiatric problems and violence who said over a month ago that he would leave Germany voluntarily.