German police said Friday a suspicious object that prompted the evacuation of a Christmas market in Potsdam has been confirmed to be an "explosive".

"Suspicions of an unconventional explosive device have been confirmed," police in Brandenburg state outside Berlin said on Twitter.

German media sources reported that a package of 40 to 59 centimeters was delivered to a pharmacy located near the Christmas market. Employees of the pharmacy who opened the package informed the police, after discovering "suspicious wires."

Potsdam police secured the Christmas market as part of preventive measures, while special forces units were also deployed to the area.

Germany is on high alert for potential terrorist attacks nearly a year after a Tunisian terrorist hijacked a truck, killed its driver, and then rammed the vehicle into a Christmas market in Berlin, killing 11 more people there.

Christmas markets opened across Germany on Monday at the start of the holiday season, fortified with security staff and concrete barriers to protect shoppers.

Germany has some 2,600 such markets, filled with sparkling Christmas trees and wooden stalls serving candied nuts, sausages, mulled wine and handicrafts.

German Interior Minister Thomas de Maiziere this week said Germany had increased information-sharing between state and federal officials and taken other steps to increase security after a series of missteps on the Berlin case.

An interior ministry spokesman this week said the risk of an attack in Europe and Germany is "continuously high".