WASHINGTON - The government warned on Tuesday of potentially life-threatening twisting of the intestines in infants vaccinated against a virus that is the leading cause of early childhood diarrhea.

The condition, called intussusception, is the same that led to the withdrawal of the first rotavirus vaccine eight years ago.

The Food and Drug Administration said it was unknown whether the recently approved vaccine, called RotaTeq, caused the 28 new cases. The condition also can occur spontaneously. Indeed, the reports don't exceed the numbers expected to occur naturally each year - the so-called background rate, the FDA said.

"It looks like this is the natural background rate that we are seeing," said Dr. Michelle Goveia, medical director for pediatric medical affairs at the vaccine's manufacturer, Merck & Co. Inc. Goveia suggested heightened concerns about the previous vaccine, made by Wyeth, prompted the FDA to act.

In Tuesday's public health notification, the agency said it wanted in part to encourage reporting of any additional cases of intestinal twisting or blockage to help it assess any risks associated with the three-shot vaccine series. It also said the vaccine's label would mention the cases of intussusception.

"It's a known serious, life-threatening adverse event that is being seen at an expected level postmarketing. But because it is so serious, we asked the company to change the label," FDA spokeswoman Karen Riley said.