Cell phones, complete with a charger and data chips, were found in the body cavities of four inmates at a maximum-security prison, and they had used the phones to direct criminal activities on the street, officials said Wednesday.

The discovery was made Tuesday at the prison in Zacatecoluca, in central El Salvador, after suspicious officials took X-rays of the inmates, federal corrections chief Jaime Villanova said.

The names of the prisoners, all members of the dangerous Mara Salvatrucha gang, were not released in order to avoid jeopardizing an ongoing investigation that began a month ago, he said.

Capt. Juan Ramon Arevalo, director of the Zacatras prison, said the gang members had introduced the cell phones, wrapped in plastic bags, into their bodies through their anuses. The phones were relatively small — about as long as an adult forefinger.

Authorities also found nine cell phone chips, each slightly larger than a fingernail, and one charger.

“Each one had a cellular with a number of chips,” Arevalo said, adding that one also had hidden a charger in his anal cavity.

The smuggled phones were found during an investigation at prisons throughout the country amid complaints from business owners of extortion by gang members.

The prisoners had changed phone chips frequently to avoid being traced, Arevalo said.