PARIS - Thousands of French troops deployed around Paris on Sunday and tourist sites stood shuttered in one of the most visited cities on Earth, while investigators questioned relatives of a suspected suicide bomber involved in the country's deadliest violence in decades.
The Islamic State group claimed responsibility for Friday's attacks on a stadium, a concert hall and Paris cafes that left 129 people dead and over 350 wounded, 99 of them seriously.
The attack had global impact. Security was heightened across France, across Europe's normally open borders, even across the ocean to New York, and how to respond to the Paris attacks became a key point among US Democratic presidential hopefuls at a debate on Saturday night.
In Britain, special forces have been deployed to back police, British newspapers reported on Sunday, as part of a wider boost in security measures.
Interior minister Theresa May did not deny the reports, telling the BBC that "arrangements" had been made to give the police military support where necessary.
Countries around the world doused their national buildings in the French colors of blue, white and red to honour the victims - or, like the Eiffel Tower and New York's Empire State Building, went dark to express their sorrow.
US President Barack Obama on Sunday called the terror attacks in Paris an "attack on the civilised world".
A candle is placed at a memorial along a police cordon set-up close to the Bataclan concert hall on Sunday, two days after a series of deadly attacks. (AFP photo)
Mr Obama, speaking at a G-20 summit in Turkey focusing on fighting terrorism, pledged US solidarity with France in the effort to hunt down the perpetrators and bring them to justice.
President Francois Hollande has said that France, which is already bombing Islamic State targets in Syria and Iraq in a US-led coalition, would increase its military efforts to crush IS and be "merciless" against the extremists.
With 3,000 extra troops mobilised to protect Paris, French authorities laboured Sunday to identify the suicide bombers and hunt potential accomplices still at large.
Paris Prosecutor Francois Molins said three groups of attackers, including seven suicide bombers wearing identical vests containing the explosive TATP, carried out the attacks that began as Parisians enjoyed a night out Friday.
The investigation sprawled well beyond France's borders, since some attackers mentioned Syria and Iraq. Authorities in Belgium arrested three people in raids linked to the Paris attacks, and a Syrian passport found next to the body of a man who attacked France's national stadium suggested that its owner passed through Greece into the European Union last month.
However, many questions remain - mainly who the other attackers were, and whether there are others still at large.
French authorities are particularly concerned about the threat from hundreds of French Islamic radicals who have travelled to Syria and returned home, possibly with dangerous skills.
Details about one attacker began to emerge: 29-year-old Frenchman Ismael Mostefai, who had a record of petty crime and had been flagged in 2010 for ties to Islamic radicalism. He was identified from fingerprints found on a finger amid the bloody carnage from a Paris concert hall, the Paris prosecutor said. A judicial official and lawmaker Jean-Pierre Gorges confirmed his identity.
Police detained his father, a brother and other relatives on Saturday night, and they were still being questioned Sunday, the judicial official said.
Authorities in Greece, meanwhile, said the holder of the Syrian passport found at the site of the stadium attack entered on Oct 3 through Leros, one of the eastern Aegean islands that tens of thousands of people fleeing war and poverty have been using as a gateway into Europe.
The same man entered Serbia from Macedonia on Oct 7 and requested asylum in Serbia, according to Serbian police.
It was not clear if the passport was real or fake, or if it belonged to the suicide bomber. The chief of the European Union border agency Frontex has said trafficking in fake Syrian passports has increased as a flood of refugees has poured into Europe.
Belgian authorities raided a Brussels neighbourhood and arrested three people near its border with France after a car with Belgian licence plates was seen close to Bataclan theatre, where at least 89 people died in a hailstorm of bullets.
A French judicial official says a Seat car with suspected links to gun attacks on Paris bars and restaurants was found by police in Montreuil, a suburb 6 kilometres east of the French capital. The official spoke Sunday on condition of anonymity because she was not publicly authorised to speak.
Struggling to keep his country calm and united after an exceptionally violent year, Mr Hollande met Sunday with opposition leaders - conservative rival and former president Nicolas Sarkozy as well as increasingly popular far-right leader Marine Le Pen, who has used the attacks on Paris to advance her anti-immigrant agenda.
After the meeting, Mr Sarkozy called for a change in France's Syria policy, suggesting the country needs to work with both Russia and the US to "destroy" the Islamic State group.
"We need everyone ... there can't be two coalitions in Syria," Mr Sarkozy said.
On the streets, the entire nation was enveloped in mourning. Flags were lowered and Notre Dame Cathedral - closed to tourists like many Paris sites - planned a special church service later Sunday for families of the victims. Well-wishers heaped flowers and notes on a monument to the dead in the neighbourhood where attackers sprayed gunfire on cafe diners and concert-goers.
Israel said on Sunday its spy services were helping France investigate the Paris gun and bomb attacks, and Israeli media suggested that intelligence being provided drew on surveillance of militant groups in Syria and Iraq.
Prime Minister Benjamin Netanyahu said he had ordered full cooperation with French and other European authorities trying to identify the perpetrators and prevent further attacks.
"The cooperation is ongoing, but in accordance with the prime minister's directive, intelligence material relevant to what happened has been relayed, and we will also deepen the cooperation," Intelligence Minister Yisrael Katz told reporters.
Meanwhile, refugees fleeing to the continent by the tens of thousands feared that the Paris attacks will prompt EU nations to throw up even more razor-wire border fences and other obstacles to their quest to start a new life.
A top European Union official insisted Sunday that the bloc's refugee policy does not need to be overhauled in the wake of the Paris attacks and urged world leaders not to start treating asylum-seekers as terrorists.
"Those who organised these attacks, and those who carried them out, are exactly those who the refugees are fleeing," European Commission President Jean-Claude Juncker told reporters at the G-20 summit in Turkey. "There is no need to revise the European Union's entire refugee policy."
Poland's incoming government declared Saturday it would not accept refugees without security guarantees but Mr Juncker urged them "to be serious about this, and not to give in (to) these basic reactions".
The Islamic State group has claimed responsibility for several recent attacks.
On Thursday, twin suicide bombings in Beirut killed at least 43 people and wounded more than 200, and 26 people died Friday in Baghdad in a suicide blast and a roadside bombing that targeted Shiites. The militant group also said it bombed a Russian plane that crashed in Egypt's Sinai Peninsula on Oct 31, killing 224 people.