Citing information from the US embassy in Damascus, Nuland said there are "credible" pictures of Ferzat's hands showing they had been broken in what she called "the most disgusting and deplorable way to send a message."
"It's not only Ali Ferzat that we are worried about. The regime has also locked up a number of other prominent dissidents to send a message," she added.
She identified them as Walid al-Buni, Nawaf Bashir, George Sabra, Mohammed Galiyun and Abdullah al-Khalil.
"These are some of the more moderate activists who have been opposing violence, and they've locked them up," Nuland said.
"How you can possibly expect a government like this to lead a transition" to democracy, she said.
Activists said masked Syrian security forces and pro-regime militiamen grabbed Ferzat in Damascus while he was returning home by car at 4:30 am (0130 GMT).
"The attackers stole the contents of his briefcase, including his drawings and other personal belongings," said Omar Idlbi of the Local Coordination Committees, which organize activists on the ground.
"He was beaten hard, notably on his hands. Passersby found him on the road to the airport and he was taken to hospital," he said.
Since the start of an anti-regime uprising in March, Ferzat, one of the Arab world's most renowned cartoonists, has published cartoons critical of the brutal crackdown on protests.
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