The US State Department said it was too early to determine whether the aid worker was targeted on Tuesday because she was an American official.
"At this point I think it's too early to say whether the person was targeted because she was a US official but obviously that possibility is on our minds," State Department spokesman Adam Ereli said.
The worker, who was not identified, was receiving medical treatment in Sudan and her injuries were not life threatening, Ereli said, adding the United States was working to have her evacuated.
Darfur has been the site of an ongoing conflict that the United Nations describes as the world's biggest humanitarian disaster.
In the armed conflict that has raged between Khartoum-backed groups and rebels, some 100,000 people have been killed.
Meanwhile, the Sudanese Vice President Ali Uthman Muhammad Taha said that his government has received an unfair share of the blame for the conflict and that more political pressure needs to be exerted on the rebels.
Taha accused the rebels of starting the war by attacking police stations and an airport. "What is needed at the moment is for them to have pressure from Europe and the US to stop," he said.