The violence Assad's regime is using against protesters is appalling, Carney added.
Sanctions likely would include a freeze on Syrian assets similar to the one the U.S. imposed on Libyan leader Muammar Qaddafi before the United Nation's approved military airstrikes in that country. It also could include a ban on business between the U.S. and Syria, U.S. officials have said.
On Monday, the regime's Army reportedly gunned down five more people, adding to an estimated 300 killed since the uprising began in February.
Carney did not rule out U.S. military action in Syria, but appeared to downplay the possibility.
He said Libya was a "unique" situation because there was an opportunity for the U.S. to prevent mass killings Qaddafi had threatened in the rebel stronghold of Benghazi and the U.S. had the support of the Arab League and several other allies including France and the United Kingdom.
The remarks sharpen the U.S. opposition to Assad's crackdown following President Obama's strongly worded condemnation Friday of the the regime's attacks against protesters who oppose it.