(ANSA) - Rome, September 12 - Italian Premier Mario Monti on Wednesday condemned the killing of the United States ambassador to Libya late Tuesday. "We condemn this heinous act with the utmost firmness," he said. According to the White House Wednesday, Ambassador J. Christopher Stevens and three American security staff were killed in a rocket attack on the US Consulate in Benghazi. Outaged over an American-produced film that allegedly ridiculed Islam's Prophet Mohammed, protesters fired guns and burned down the consulate, witnesses and the U.S. State Department said. "We will remain at the side of the authorities of the new democratic Libya, who will resist all efforts to take the country's new course hostage," said Monti.