KINSHASA (Reuters) - Police in Congo have arrested 13 suspected sorcerers accused of using black magic to steal or shrink men's penises after a wave of panic and attempted lynching triggered by the alleged witchcraft.

Reports of so-called penis snatching are not uncommon in West Africa, where belief in traditional religions and witchcraft remains widespread, and where ritual killings to obtain blood or body parts still occur.

Rumors of penis theft began circulating last week in Kinshasa, Democratic Republic of Congo's sprawling capital of some 8 million inhabitants. They quickly dominated radio call-in shows, with listeners advised to beware of fellow passengers in communal taxis wearing gold rings.

Purported victims, 14 of whom were also detained by police, claimed that sorcerers simply touched them to make their genitals shrink or disappear, in what some residents said was an attempt to extort cash with the promise of a cure.

"You just have to be accused of that, and people come after you. We've had a number of attempted lynchings. ... You see them covered in marks after being beaten," Kinshasa's police chief, Jean-Dieudonne Oleko, told Reuters on Tuesday.

Police arrested the accused sorcerers and their victims in an effort to avoid the sort of bloodshed seen in Ghana a decade ago, when 12 suspected penis snatchers were beaten to death by angry mobs. The 27 men have since been released.

"I'm tempted to say it's one huge joke," Oleko said.

"But when you try to tell the victims that their penises are still there, they tell you that it's become tiny or that they've become impotent. To that I tell them, 'How do you know if you haven't gone home and tried it'," he said. 

Some Kinshasa residents accuse a separatist sect from nearby Bas-Congo province of being behind the witchcraft in revenge for a recent government crackdown on its members.

"It's real. Just yesterday here, there was a man who was a victim. We saw. What was left was tiny," said 29-year-old Alain Kalala, who sells phone credits near a Kinshasa police station.

(Editing by Nick Tattersall and Mary Gabriel)