France is stepping up security after three days of violent lone-wolf attacks.<br/> <br />The incidents have left about 30 wounded and reignited fears of attacks by Islamist radicals.<br/> <br />French Prime Minister Manuel Valls says the country faces a terrorist threat.<br/> <br />(SOUNDBITE) (French) FRENCH PRIME MINISTER, MANUEL VALLS, SAYING:<br/> <br />"There is, as you know, a terrorist threat to France. We -- along with the Interior Minister -- have been saying it for a long time. It's without a doubt, the major challenge of our times."<br/> <br />The most recent attack came Monday night in Nantes where a man plowed his van into a crowded Christmas market, injuring at least 10 people.<br/> <br />On Saturday a stabbing wounded three police officers, and on Sunday another man drove into crowds.<br/> <br />In these first two incidents, the perpetrators yelled "Allahu Akbar".<br/> <br />Valls says investigating the attacks is a top priority.<br/> <br />(SOUNDBITE) (French) FRENCH PRIME MINISTER, MANUEL VALLS, SAYING:<br/> <br />"Th
