Washington ? The government rejected over-the-counter sales of morning-after birth control Thursday, citing concern about young teenagers’ use of the pills. But regulators left open the possibility they will reconsider.

Proponents immediately accused the Food and Drug Administration of bowing to conservative political pressure — noting the agency had overruled its own scientific advisers, who had overwhelmingly called easier access to emergency contraception a safe way to prevent some abortions.

In a Thursday letter to Barr Laboratories, the FDA said there wasn’t evidence that teens younger than 16 could safely use the pills without a doctor’s guidance.

Warned of FDA’s teen concern in February, Barr had proposed allowing nonprescription sales for everyone 16 and older but requiring a prescription for anyone younger.

Such a step, which presumably would require drugstores to check customers’ ages, has never been tried. The FDA said the company didn’t provide many details, making it impossible to decide if such a program would be legal and doable.

But Thursday, FDA officials left open the door for Barr to try again, telling the company what information they would need to reconsider: either data showing young teens could use the pills safely without a prescription, or details on how to make the mixed-marketing approach work.

Barr chief executive Bruce Downey said the company would rapidly pursue one or both options — even as it more actively advertises its prescription morning-after brand, called Plan B, so more women know that taking the pills within 72 hours of intercourse can greatly reduce their risk of pregnancy.