Lagos, Nigeria (CNN) -- Police raided a clinic in southeast Nigeria and rescued about 30 girls allegedly used in a "baby industry" in which they would give birth to children who then would be sold, authorities said Thursday.

"There are about 30 pregnant young ladies -- the eldest was 20 years old," said Geoffrey Ogbonna, a police spokesman. "Some belong in secondary, even in primary school."

In addition to the expecting mothers, 12 children were found at the clinic ranging in age from 2 to 12 years old, according to Arinze Orakwue, a spokesman for the National Agency for the Prohibition of Traffic in Persons. It was not clear whether the children found were related to the pregnant girls and women.

Orakwue called the operation of the clinic, which was officially registered, "a failure of oversight."

Police stormed the Cross Foundation clinic in Abia state over the weekend after receiving a tip, but no babies were found at the location, the spokesman said.

Authorities believe there were cases in which babies were sold for between 100,000 and 150,000 naira ($640 to $960), with the women receiving about $131, according to Ogbonna.

Some of the women had unwanted pregnancies and wanted to get rid of their babies, while others were impregnated as part of the operation of the clinic's business, Orakwue said.

A doctor arrested at the location said the babies had been handed over to social welfare for adoption.

Police said the women seized were not cooperating.

Only one of the women has talked so far, and she said her friend took her to the clinic, according to Ogbonna.

"They do not want to open up," he said.

The investigation continues, police said.