"Our postal police [service] is at the cutting edge and it is sifting the Web to find the heinous people who are celebrating someone else's death," Salvini said, as quoted by the Ansa news agency, promising "immediate arrest for anyone who has been rejoicing online over the last few hours."
READ MORE: Strasbourg Gunman Shouted 'Allahu Akbar', Was Injured During Attack — Prosecutor
As many as 3 people were killed and 13 others injured on Tuesday after a gunman opened fire near Strasbourg's Christmas market. The shooter is still on the run.
Media has reported that the suspect is a 29-year-old native of Strasbourg, previously known to police for past offences in Germany and France, as well as for radical Islamist views.