Police say a recent grenade attack on an asylum seekers' home in Germany wasn't triggered by hatred on refugees, but suspect it was caused by rivalry between different companies involved in providing safety for asylum centers.

Police in Villingen-Schwenningen in the Black Forest said late Tuesday that they detained four suspects. They did not reveal names of the four men, but only said they were migrants from eastern Europe.

Police did not give any further details, but said "conflicts between security companies could be the cause" for the attack.

The grenade was thrown over the fence of the asylum home the night of Jan. 28-29 and landed next to the container of the security staff. It didn't explode, and a bomb squad destroyed it in a controlled explosion.