It would sue U.S. fast-food giant McDonald's for handing out toys with Happy Meals, the Center for Science in the Public Interest said on Tuesday.

The toys unfairly "lure small children into McDonald's" in a marketing ploy that is "illegal under various state consumer protection laws," CSPI has said.

CSPI, defining itself as a nutrition watchdog group, said it informed McDonald's Tuesday of its intention to file suit.

CSPI litigation director Stephen Gardner said in a statement, "McDonald's is the stranger in the playground handing out candy to children."

He said, "McDonald's use of toys undercuts parental authority and exploits young children's developmental immaturity."

McDonald's pledged in 2007 not to advertise meals that have more than 600 calories to children. The pledge included limits on percentages of fat and sugar content in items it would market targeting a young demographic group, CSPI's statement has said. (With Inputs from Agencies)