U.S. officials on March 21 said they were watching the case of Abdul Rahman closely, but did not directly request that the trial be ended.
Undersecretary of State Nicholas Burns said he hoped the Afghan constitution, which he said gives Afghan citizens the right to choose their faith, will be upheld.
NATO allies Italy, Canada, and Germany, who all have soldiers serving in Afghanistan, have also voiced concern about the case.
Afghan Foreign Minister Abdullah Abdullah, who has been visiting Washington, acknowledged international concerns but said the case was a question for Afghanistan's judiciary.
Rahman, who lived in Germany for years, was detained after his family complained to authorities that he had converted to Christianity in violation of Islamic sharia law.
(compiled from agency reports)