Three teams of gunmen and suicide bombers staged coordinated attacks across Paris overnight Friday that killed 129 people, in what President François Hollande called an "act of war" by jihadist militants, French prosecutors said Saturday. Hollande declared a state of emergency early on Friday, ordering police and troops into the streets, and set three days of official mourning as a stunned nation sought to comprehend the simultaneous assault on restaurants, a concert hall and the national soccer stadium on a busy Friday evening. As a cross-border investigation gathered pace, prosecutors said the slaughter appeared to involve a multinational team with links to the Middle East, Belgium and possibly Germany, as well as home-grown French roots. The Islamic State (IS) group claimed the attack, saying it was in retaliation for French military action in Syria and Iraq. Ominously, Greek officials said one and perhaps two of the assailants had passed through Greece from Turkey alongside masses of desperate Syrian refugees fleeing violence in their homeland. The worst carnage was unleashed as three gunmen systematically killed at least 89 people at a rock concert by an American band at the Bataclan concert hall before detonating explosive belts as anti-terrorist commandos launched an assault, officials said. Some 40 more people were killed in five other attacks in the Paris region, including a double suicide bombing outside the Stade de France stadium, where Hollande and the German foreign minister were watching a friendly football match. By Saturday night, 99 people were still in critical condition. The bloodshed came as France, a founder member of the US-led coalition waging air strikes against the IS group, was already on high alert for terrorist attacks, raising questions about how such a complex conspiracy could go undetected. It was the worst such attack in Europe since the Madrid train bombings of 2004, in which Islamists killed 191 people. Where we stand now One attacker identified French media identified one of seven attackers as a 29-year-old Frenchman of Algerian origin from the Paris suburbs. The suspect, who helped kill scores of people in the Bataclan, held a criminal record and was known to the authorities for possibly having been radicalised as far back as in 2010. He travelled to Syria for a few months in between 2013 and 2014. Attacks were coordinated Paris Prosecutor François Molins said on Saturday that the three attacks were coordinated, that the seven assailants involved wore identical suicide vests fitted with batteries and a detonator and were carrying a charge of TATP (triacetone triperoxide). They also carried semi-automatic rifles similar to the ones used in the Charlie Hebdo attacks in January. French PM vows to ‘destroy' enemy French Prime Minister Manuel Valls vowed to "destroy" those behind the attacks late on Saturday, saying "we are at war, and because we are at war we are taking exceptional measures" in an interview with French TV station TF1. "We will strike this enemy to destroy him. In France and in Europe, we'll chase the authors of this act, and also in Syria and Iraq. We will win this war," he said. Victims' names start to emerge Twenty-four hours after the attacks broke out many of the victims had been identified and names started to emerge. An American, A Briton, two Mexicans and three Chileans were identified among the victims. Many people continue to search for their loved ones using the Twitter hashtag #rechercheparis. Arrests made in Belgium Belgium's federal prosecutor's office said authorities made three arrests on Saturday linked to the attacks. Spokesman Jean-Pascal Thoreau said the arrests came after a rental vehicle with Belgian license plates was seen close to the Bataclan theatre on Friday night. Police organised several raids in the St. Jans Molenbeek neighbourhood in Brussels on Saturday. Family members of attacker detained The spokeswoman for the Paris prosecutor's office said late on Sunday that the brother and father of one of the attackers — a French national born in the Paris suburbs — had been detained. Syrian passport found Prosecutor Molins said the identity of a person in a Syrian passport found near one of the attacker's bodies was not known to French intelligence services. Coordinated response Along with the FBI and other agencies, US Justice Department attorneys are working with French authorities to obtain further information that may be relevant to the Paris attacks, a Justice Department official said on Saturday.