BEIJING — China has broken up a gang that offered illegal services to determine the sex of unborn children so that women could abort those they did not want, the country's health ministry said Sunday.

Three decades of strict family planning have bolstered a traditional bias for male offspring, seen as the main support of elderly parents and heirs to the family name, and have resulted in abortions, killings, or abandonment of girls and trafficking of male and female children.

The health ministry said the crackdown netted 10 people who since 2010 had operated a service sending women from all over the country to a clinic in the central city of Zhengzhou to find out the sex of their unborn child.

Last year alone, more than 1,000 women used the service, it said, although it did not say how many abortions resulted.

One of the ringleaders has already received a jail term of 3-1/2 years and fined $16,500, with the rest getting slightly shorter sentences.

The ministry said it was the biggest case of its kind in the past few years.

"This went on for a long time, covering a wide area and involved many people. It was malicious, had serious results and was a great threat to society," it added.

The problem is widespread, the ministry warned, adding that it faced a "serious situation" in trying to end such abuses.

The government has tried for years to address the issue, which has lead to serious population imbalances in some parts of China, particularly its wealthy coastal provinces.

Last week a court handed down a suspended death sentence for a doctor who sold seven newborns to human traffickers, in a case that ignited anger over rampant child trafficking.

The imbalance has created criminal demand for abducted or bought baby boys, but also for baby girls destined to be future brides, attracting rich dowries in parts of the country where there are too few women for all the men seeking wives.

While the government late last year announced a relaxation of its "one child" policy, many curbs remain, with Beijing saying family planning is still a key way to ensure China does not produce too many children to burden limited resources.