The world may shut doors on refugees. The US, a nation of immigrants, is showing signs of nervousness with more than half the nation's governors -- 26 states – opposing entry of Syrian refugees into their states. The final say on this contentious immigration issue rests with the federal government but the states can make the acceptance process much more difficult.

States protesting the admission of refugees range from Alabama and Georgia, to Texas and Arizona, to Michigan and Illinois, to Maine and New Hampshire. Most of these states have Republican governors.

The announcements came after authorities revealed that at least one of the suspects believed to be involved in the Paris terrorist attacks entered Europe among the current wave of Syrian refugees. Some leaders say they either oppose taking in any Syrian refugees being relocated as part of a national program or asked that they be particularly scrutinized as potential security threats.

Only 1,500 Syrian refugees have been accepted into the United States since 2011, but the Obama administration announced in September that 10,000 Syrians will be allowed entry next year.

Meanwhile, French president Francois Hollande called on the United States and Russia to join a global coalition to destroy Islamic State following the attacks across Paris, and announced a wave of measures to combat terrorism in France.

"France is at war," Hollande told a joint session of Parliament at the Palace of Versailles on Monday, promising to increase funds for national security and strengthen anti-terrorism laws in response to the suicide bombings and shootings that killed 129.

"We're not engaged in a war of civilisations, because these assassins do not represent any. We are in a war against jihadist terrorism which is threatening the whole world," he told a packed, sombre chamber.

Hollande pledged that French fighter jets would intensify their assaults and said he would meet US president Barack Obama and Russian president Vladimir Putin in the coming days to urge them to pool their resources.

"We must combine our forces to achieve a result that is already too late in coming," the president said.

Speaking in Turkey at the same time as Hollande, Obama called Friday's attacks a "terrible and sickening setback", but maintained that the US-led coalition was making progress.

"Even as we grieve with our French friends ... we can't lose sight that there has been progress," Obama said at a Group of 20 summit, ruling out sending in ground troops.

US Secretary of State John Kerry, visiting Paris to pay respects to those killed in the attacks, said: "Tonight we are all Parisians," and pledged the United States would stand "shoulder to shoulder" with France. He is due to meet Hollande today.

Much of France came to a standstill at midday for a minute's silence to remember the dead, many of whom were young people killed as they enjoyed a night out. Metro trains stopped, pedestrians paused and office workers stood at their desks.

Islamic State has claimed responsibility for Friday's coordinated attacks, saying they were in retaliation for France's involvement in US-backed air strikes in Iraq and Syria. The US-led coalition has been bombing Islamic State for more than a year. Russia joined the conflict in September, but Western officials say it has mainly hit foreign-backed fighters battling Syrian president Bashar al-Assad, not Islamic State.

Islamic State warned in a video on Monday that any country hitting it would suffer the same fate as Paris, promising specifically to target Washington.

Investigators have identified a Belgian national living in Syria as the possible mastermind behind the attacks, which targeted bars, restaurants, a concert hall and soccer stadium. A source close to the investigation said Belgian national Abdelhamid Abaaoud, currently in Syria, was suspected of having ordered the Paris operation. RTL Radio said Abaaoud was a 27-year-old from the Brussels district of Molenbeek, home to many Muslim immigrants and a focal point for Islamist radicalism in recent years.

Police in Brussels have detained two suspects and are hunting Salah Abdeslam, a 26-year-old Frenchman based in Belgium. One of his brother's died in the Paris assault, while a third brother was arrested at the weekend but later released.

The Belgian interior ministry issued two new photographs of Abdeslam late on Monday.

Police in France named two of the French attackers as Ismael Omar Mostefai, 29, from Chartres, southwest of Paris, and Samy Amimour, 28, from the Paris suburb of Drancy.

France believes Mostefai, a petty criminal who never served time in jail, visited Syria in 2013-2014. His radicalisation underlined the trouble police face trying to capture an elusive enemy raised in its own cities.

Prosecutors have identified five of the seven dead assailants - four Frenchmen and a foreigner fingerprinted in Greece last month. His role in the carnage has fuelled speculation that Islamic State took advantage of a recent wave of refugees fleeing Syria to slip militants into Europe.

French Interior Minister Bernard Cazeneuve told reporters police had arrested nearly two dozen people and seized arms, including a rocket launcher and automatic weapons, in 168 raids overnight.

CIA Director John Brennan warned on Monday that Islamic State militants may have similar operations ready to launch, but foiling those plots could prove difficult because Europe's intelligence and security resources are severely stretched.