Pharmacist holds package of "Plan B" emergency contraceptive tablets (AP)

WASHINGTON (AP) -- The nation's health secretary says young teenagers cannot buy the Plan B morning-after pill without a prescription -- a surprise move overruling her own experts, who were preparing to let it be sold on drugstore shelves like condoms.

The pill can prevent pregnancy if taken soon enough after unprotected sex. Currently, only those 17 or older can buy Plan B One-Step without a prescription, if they show a pharmacist proof of age.

The Food and Drug Administration was preparing to lift that age limit and let the emergency contraceptive be sold over the counter to anyone. But Health and Human Services Secretary Kathleen Sebelius overruled the agency, saying she was concerned that very young girls couldn't properly understand how to use it without guidance from an adult.