French troops policed the streets in the aftermath as investigators scoured six bloody crime scenes and shock hovered over the city after the deadliest attack on French soil since Nazis invaded in World War II. French President Francois Hollande vowed a “Merciless” response to the slaughter as ISIS claimed responsibility.

The assailants, working in three teams, attacked concert-goers, cafe diners and soccer fans in at least six locations in the French capital.

French media partially identified two of the attackers as Ismail M. and Abbdul Akbak B. A former French official confirmed to NBC News that those partial identities are correct.

Belgium’s justice minister said Saturday that several arrests connected to the attacks were made in Brussels, the Associated Press reported.

Speaking early Saturday, Hollande pointed the finger at ISIS for orchestrating the “Cowardly” attacks which he described as an “Act of war committed by a terrorist army” and organized from abroad. He said France remained “Unbreakable,” calling for “Unity and courage.”

ISIS released an undated video Saturday urging Muslims who are unable to wage holy war in Syria to carry out attacks in France, according to an unclassified FBI document.

Molins said the attackers “Referred to Syria and Iraq” during the attack.

The attacks Friday hit a nation still reeling from January’s three-day terror spree that left 20 people dead – including three attackers, who opened fire at the offices of Charlie Hebdo magazine and later laid siege on a kosher supermarket.

France has seen several smaller-scale attacks or attempts this year, including an incident on a high-speed train in August in which American travelers thwarted an attempted attack by a heavily armed man.