PARIS — A teenage Roma boy lay in a coma in a hospital here on Tuesday after being abducted from a shantytown and beaten last week, apparently in retaliation for what his assailants thought were thefts he committed in a nearby housing project, the French authorities said.

Politicians and rights groups condemned the attack, which police and judicial officials said involved as many as a dozen people. No racial motives were immediately apparent, and investigators have made no arrests.

President François Hollande, whose leftist government has sharply accelerated the destruction of Roma camps, called the abduction and beating “beyond words and unjustifiable.” Mr. Hollande did not call the attack a hate crime, however.

The boy, identified by law enforcement officials only as Darius, a 16-year-old Romanian citizen, was found abandoned in a shopping cart at the edge of a highway late Friday in Pierrefitte-sur-Seine, a poor, heavily immigrant suburb north of Paris.