PARIS, March 15 (Reuters) - Two young men have been placed under formal investigation in France for planning a "deadly and antisemitic" attack, the counterterrorism prosecutor's office (PNAT) ?said in a statement on Sunday. The suspects, a 22-year-old engineering student ?and an unemployed 20-year-old who are brothers, were arrested last Tuesday after police found a semi-automatic firearm, a bottle of acid and an ISIS flag in their ?car during a roadside police stop near a prison in northern ?France, PNAT said. It gave no details about the nature ?of the planned attack or its target. Sign up here. The two...