BERLIN (AP) — German police say nine wooden spikes topped with parts of a dead pig were planted on a plot of land where Muslims are planning to build a mosque in the eastern city of Erfurt.

The dpa news agency reported Monday that the 1.5 meter- (4.9 foot-) tall stakes were topped with half of a pig's head, pig feet, and pig bowels among other things. The animals are considered unclean by Muslims.

Police say whoever was responsible is unknown.

There have been repeated protests against the construction of the Ahmadiyya mosque in Erfurt, including one by protesters who erected large Christian crosses on a neighboring property.

Erfurt police and the imam of the Erfurt community could not immediately be reached for comment.