The Rev. Jesse Jackson was hospitalized and undergoing tests Thursday after complaining of severe stomach pains.

Jackson told The Associated Press that he entered Northwestern Memorial Hospital on Wednesday after falling ill earlier in the week.

Doctors told him he has viral gastroenteritis but were conducting more tests. The 66-year-old civil rights leader said he was feeling much better Thursday morning but wasn't sure when he would be released.

Jackson said he was campaigning for Sen. Barack Obama and doing voter registration in Georgia when he began to feel ill after apparently becoming dehydrated.

According to the federal Centers for Disease Control and Prevention, gastroenteritis is an inflammation of the stomach and small and large intestines. It isn't considered serious for most people.