A French tourist beat his 4-year-old daughter's head against the stone base of a Rome monument so hard the child was left in a coma, police said Sunday.

Blood still stained the travertine pavement of the Altar of the Nation, a towering monument to Italy's war victims, hours after the savage beating late Saturday night in Piazza Venezia in the heart of Rome.

Bambino Gesu pediatric hospital said the child was comatose with severe head injuries when she was admitted shortly before midnight.

"Her condition is stable but very critical," Daniela Perrotta, from the hospital's anesthesia department, told reporters outside the hospital.

Carabinieri Lt. Col. Antonello Casarsa said the man, identified as Julien Monnet, 37, repeatedly struck the head of his daughter, Luna, against the stone after a traffic officer asked to see some identification. A Canadian tourist had told police the man was acting strangely toward the child.

"He was holding the child in an unhealthy way. The child was crying and screaming," the traffic officer, Anna Esposito, told Italian state TV.

When Esposito approached the man, she said, the man quickened his step, then said something she couldn't understand when she asked him what he was doing.

"He was holding the girl by her arm and then started striking her [head] against the stone," Esposito said, looking shaken. The Canadian grabbed the child, Esposito said, while she struggled to hold the man and called for reinforcements.

"He was like a furious beast," Esposito said.

After the man was blocked by passers-by, he tried to break loose and strike his own head against the monument base, but onlookers stopped him, Casarsa said.

The man's backpack contained medicine indicating he was undergoing psychiatric treatment, Casarsa said.

Casarsa said Monnet lives with the child's mother near Paris.

Monnet was arrested for investigation of causing grave injury and taken to Rome's Regina Coeli jail, Casarsa said. He appeared to be in a state of shock when arrested, Casarsa said.

The mother was vacationing in Turkey, and was flying to Rome after being called by police. The woman told police she believed Monnet and the girl were still in France and had no idea they had traveled to Rome, Casarsa said.