As the case moves through the appeal process "we hope it is conducted in a manner that affords protection of due process, fairness and justice" to the defendant, U.S. State Department deputy spokesman Philip T. Reeker said Tuesday.
An Islamic high court in northern Nigeria rejected an appeal by the woman, and her lawyers said they planned to appeal to a higher Islamic court. If that fails, they can appeal to the Supreme Court, where the case would force a showdown between Nigeria's constitutional and religious authorities.
The introduction of Islamic law, or Shariah, in a dozen states has triggered confrontations between the country's Christians and Muslims.
Amina Lawal, 30, was first sentenced in March after giving birth to a daughter more than nine months after divorcing.