PARIS (Reuters) - French prosecutors said on Saturday that three coordinated teams of gunmen and suicide bombers carried out a wave of attacks across Paris that killed 129 people in what President Francois Hollande called an "act of war" by Islamic State.
Hollande declared a state of emergency, 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 - claimed by Islamic State as revenge for French military action in Syria and Iraq - appeared to involve a multinational team with links to the Middle East, Belgium and possibly Germany as well as home-grown French roots.
Ominously, Greek officials said one and perhaps two of the assailants had passed through Greece from Turkey alongside Syrian refugees fleeing violence in their homeland.
In the worst carnage, three gunmen systematically killed at least 89 people at a rock concert by an American band at the Bataclan theater 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 soccer international. By Saturday night, 99 people were still in critical condition.
The bloodshed came as France, a founder member of the U.S.-led coalition waging air strikes against Islamic State, 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.
Hollande said the attacks had been organized from abroad by Islamic State, with internal help.
Three people were arrested in Belgium as part of an anti-terrorism probe centered on a Belgian hired car found near the site of one of the Paris attacks, Belgian prosecutors said. It was one of two vehicles used in a string of attacks in central Paris within the space of less than an hour.
Sources close to the inquiry said one of the dead gunmen was French with ties to Islamist militants and had been under surveillance by the security services. French media said the man's brother and father had been were arrested on Saturday
A man arrested in Germany's southern state of Bavaria this month after guns and explosives were found in his car may also be linked to the Paris attacks, Bavaria's state premier said.
The holder of a Syrian passport found near the body of one of the suicide bombers outside the soccer stadium passed though the Greek island of Leros in October, a Greek minister said.
A Greek police source said the man had arrived in Leros with 69 refugees, where he was registered and had his fingerprints taken. Police declined to give his name. A Greek government source later said that a second suspected Paris attacker was also very likely to have passed through Greece.
If confirmed, the infiltration of militants into the flow of refugees to carry out attacks in Europe could have far-reaching political consequences.
The attacks fueled a debate raging in Europe about how to handle the influx of hundreds of thousands of refugees and other migrants propelled by civil war in Syria, Iraq and Libya.
German Chancellor Angela Merkel and the European Commission have been pressing EU partners to ease Berlin's burden by taking in quotas of refugees.
However, in a sign of potential divisions ahead, Poland said that the attacks meant it could not now take its share of migrants under the European Union relocation plan.
The carnage on the streets of the French capital followed recent attacks claimed by Islamic State: the apparent downing of a Russian passenger plane in Egypt, where 224 people died, and bombings in Lebanon in which 43 died. Turkey has also pointed the finger at Islamic State over a bomb attack on a rally in Ankara last month in which more than 100 people were killed. All the attacks were linked to the war in Syria.
Prime Minister Manuel Valls said France had no intention of halting its air strikes. Turkish President Tayyip Erdogan urged world leaders gathered for a summit in Turkey starting on Sunday to prioritize the fight against terrorism, saying the Paris attacks showed the time for words was now over.
Hollande pulled out of the G20 summit after declaring the first nationwide state of emergency since 1961. France will be represented by its foreign and finance ministers.
"Faced with war, the country must take appropriate action," the president said in a solemn address after meeting security chiefs.
"France will be merciless towards these barbarians from Daesh," Hollande said, using an Arab acronym for Islamic State.
Flags flew at half-mast and cinemas, theaters and other places of entertainment were closed, although schools and universities will reopen as normal on Monday.
With the capital on edge, armed police rushed to a luxury hotel near the Eiffel Tower on Saturday evening, evacuated the building, sealed off a wide perimeter and closed nearby metro stations, only to say it had been a false alarm.
Speaking after peace talks on Syria in Vienna, U.S. Secretary of State John Kerry said: "We are witnessing a kind of medieval and modern fascism at the same time".
In its claim of responsibility, Islamic State said the attacks were a response to France's military campaign.
It also distributed an undated video in which a bearded militant warned in Arabic: "As long as you keep bombing, you will not live in peace. You will even fear traveling to the market."
Updating the casualty toll, the Paris prosecutor said 129 people had been killed and 352 wounded, of whom 99 remained critical. Six attackers blew themselves up and one was shot by police. There may have been an eighth attacker, but this was not confirmed.
The dead included one U.S. citizen, one Swede, one Briton, two Belgians, two Romanians and two Mexicans, their governments said.
Relatives and friends scoured Paris hospitals in search of people missing since Friday evening and believed to have gone to the Bataclan concert hall. Some anguished next of kin said their relatives were neither on the confirmed death toll nor among the wounded registered in hospitals.
Sylvestre, a young man who was at the Stade de France when bombs went off there, said he had been saved by his cellphone, which he was holding to his ear when a metal bolt hit it.
Hollande temporarily reimposed border controls as part of the state of emergency to stop perpetrators escaping or new attackers entering the country.
Local sports events in Paris were suspended, stores closed, the rock band U2 canceled a concert, and schools, universities and municipal buildings stayed shut.
Emergency services were mobilized, police leave was canceled, 1,500 army reinforcements were drafted into the Paris region and hospitals recalled staff to cope with casualties.
However, France said a global climate change summit in Paris at the end of the month would go ahead, amid heightened security.
France has been on high alert since Islamist gunmen attacked the satirical weekly Charlie Hebdo and a kosher supermarket in January, killing 18 people.
Those attacks briefly united France in defense of freedom of speech, with a mass demonstration of more than a million people. But that unity has since broken down, with far-right populist Marine Le Pen gaining on both mainstream parties by blaming France's security problems on immigration and Islam.
World leaders responded to the attacks in Paris with defiant pledges of solidarity. From Barack Obama to Vladimir Putin and across Europe and the Middle East, leaders offered their condolences.
France ordered increased security at its missions abroad. Britain, Germany, Italy, Russia, Belgium, Hungary and the Netherlands all tightened security measures.
British police said the evacuation of London's Gatwick Airport on Saturday was connected to the discovery of a possible firearm in a bin, and that a 41-year-old man from France had been arrested.
Additional reporting by Geert de Clercq, Jean-Baptiste Vey, Emmanuel Jarry, Elizabeth Pineau, Julien Pretot and Bate Felix Tabi-Tabe; Writing by Giles Elgood and Paul Taylor; Editing by Sonya Hepinstall and Kevin Liffey