The US administration has filed a last-ditch bid to delay a court ruling that would allow girls and young women to buy the morning-after pill without a prescription.

A US district court ruled last month that a 2011 decision by the chief of US Health and Human Services to require teens under 17 to obtain a prescription was "politically motivated" and "scientifically unjustified".

The ruling ordered the Food and Drug Administration to make levonorgestrel-based emergency contraception available over the counter to people under 17 without a doctor's prescription.

Emergency contraceptives contain the same active ingredients as birth control pills but at higher doses, and can prevent pregnancy if taken within 72 hours of unprotected intercourse.

The appeal filed on Monday in the Court of Appeal in Manhattan prevents Judge Korman's ruling from taking effect until May 28.