PARIS — French President Francois Hollande called on the United States and Russia on Monday to join a global coalition to destroy Islamic State after 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, 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 civilizations, 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, somber chamber.

Parliamentarians gave Hollande a standing ovation before spontaneously singing the “Marseillaise” national anthem in a show of political unity after the worst atrocity France has seen since World War II.

Islamic State has claimed responsibility for Friday’s coordinated attacks, saying they were in retaliation for France’s involvement in U.S.-backed airstrikes in Iraq and Syria.

Hollande pledged that French fighter jets would intensify their assaults and said he would meet with U.S. 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.

The U.S.-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.

Speaking in Turkey at the same time as Hollande, Obama called Friday’s attacks a “terrible and sickening setback,” but maintained that the U.S.-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.

U.S. 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 against Islamic State militants. He is due to meet Hollande on Tuesday morning.

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.

In a sign of life slowly returning to normal, schools and museums reopened after a 48-hour shutdown, as did the Eiffel Tower, which lit up the night sky in the red, white and blue colors of the French flag after two days of darkness.

Islamic State threats

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.

“Friday’s act of war was decided upon and planned in Syria, prepared and organized in Belgium and carried out on our territory with the complicity of French citizens,” said Hollande.

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 fueled speculation that Islamic State took advantage of a recent wave of refugees fleeing Syria to slip militants into Europe.

Police believe one attacker is on the run, and suspect at least four people helped organize the mayhem.

French Prime Minister Manuel Valls told RTL Radio, “We know that more attacks are being prepared, not just against France but also against other European countries.” He added, “We are going to live with this terrorist threat for a long time.”

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

“We say to the states that take part in the crusader campaign that, by God, you will have a day God willing, like France’s and by God, as we struck France in the center of its abode in Paris, then we swear that we will strike America at its center in Washington,” one man in the video said.

It was not immediately possible to verify the authenticity of the video.

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.

“Let this be clear to everyone, this is just the beginning, these actions are going to continue,” he said.

Hollande said he would create 5,000 jobs in the security forces, boost prison service staff by 2,500 and avoid cuts to defense spending before 2019. He acknowledged that would break EU budget rules, but said national security was more important.

He also said he would ask parliament to extend for three months a state of emergency he declared Friday, which gives security forces sweeping powers to search and detain suspects.

CIA Director John Brennan warned 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.

Manhunt

A source close to the investigation said Belgian national Abdelhamid Abaaoud, currently in Syria, was suspected of having ordered the Paris operation. “He appears to be the brains behind several planned attacks in Europe,” the source told Reuters.

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 brothers died in the Paris assault, while another was arrested over the weekend but later released.

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 2013-14. His radicalization underlined the trouble police face trying to capture an elusive enemy raised in its own cities.

“He was a normal man,” said Christophe, his neighbor in Chartres. “Nothing made you think he would turn violent.”

Latest official figures estimate that 520 French nationals are in the Syrian and Iraqi war zones, including 116 women. Some 137 have died in the fighting, 250 have returned home and around 700 have plans to travel to join the jihadist factions.

The man stopped in Greece in October was carrying a Syrian passport in the name of Ahmad Al Mohammad. Police said they were still checking to see if the document was authentic, but said the dead man’s fingerprints matched those on record in Greece.

Greek officials said the passport holder had crossed from Turkey to the Greek islands last month and then registered for asylum in Serbia before heading north, following a route taken by hundreds of thousands of asylum seekers this year.

His role in the mission has reignited a fierce debate in Europe about how to tackle a continuing influx of refugees, with anti-immigrant parties calling for borders to be closed against the flood of newcomers fleeing the Middle East.