Letters containing anti-Muslim threats were sent to three mosques in Germany, according to officials.
The Turkish-Islamic Union for Religious Affairs (DITIB), which runs the three mosques in northwestern Germany, condemned the racist incident and called on authorities to take action against Islamophobia.
"These heinous acts have deeply saddened us and our neighbors," the chairs of the DITIB mosque associations in Bochum, Castrop-Rauxel and Recklinghausen said in a joint statement.
"We are worried. The continuation of similar attacks will cause serious concerns in the community. The perpetrator or perpetrators must be apprehended and brought to justice as soon as possible," they said.
The packages sent to the mosques in the three cities contained racist messages, burned pages of the Quran, Islam's holy book, pork and feces, according to the officials.
Germany is facing a rise in anti-Muslim racism and violence in recent years, fueled by the propaganda of far-right political parties and movements.
In the first half of 2023, police recorded 258 anti-Muslim crimes, including attacks on mosques, cases of bodily harm, and threatening letters.
A country of more than 84 million, Germany has the second-largest Muslim population in Western Europe after France. It is home to more than 5 million Muslims, according to official figures.