LONDON — The killing of at least 12 people at a French newspaper that received threats because of its depiction of Islam stands to exacerbate already burgeoning anti-Muslim sentiment in Europe.

The shooting by masked gunmen at the satirical weekly Charlie Hebdo in eastern Paris adds to a tense environment, with an anti-immigrant party dominating in France, mosque burnings in Sweden and thousands marching in Germany decrying the “Islamization” of the west.

“Any incident like the one in Paris will only be fuel to the fire,” Joerg Forbrig, the senior program director at the German Marshall Fund of the United States, said by phone from Berlin. “It will be welcomed as a ‘told-you-so’ episode by radical movements saying Islam is a threat to our countries.”

The suspected attackers – at least one of whom shouted “Allahu Akbar,” or “God is great” in Arabic – were named by police Wednesday, but no motive has been confirmed. Charlie Hebdo’s offices were firebombed in 2011 when it featured the Prophet Muhammad as a “guest editor.” The magazine sparked worldwide outrage among Muslims in 2012 after publishing cartoons mocking the prophet.

The leader of the anti-Islam Freedom Party in the Netherlands, Geert Wilders, took aim at the Dutch and European political establishments and Dutch Prime Minister Mark Rutte.

“When will Rutte and other western government leaders finally get the message: It’s war,” Wilders said Wednesday.

Europe’s political establishment, struggling to respond to the region’s sagging economy and near-record unemployment, has been buffeted by insurgent factions that have exploited a rise in sentiment against foreigners and Muslims.

“Europe is in the grip of so much tension over the question of Islam and immigration,” said Shada Islam, director of policy at the Friends of Europe advisory group in Brussels. “There is the danger in the immediate aftermath that this is going to strengthen the anti-immigration campaigns, but you have to have a longer-term strategy when the emotions subside.”

In France, polls show the anti-immigration National Front taking the lead in a first-round vote over established parties. The National Front has gained at least some traction by voicing fear of the spread of Islam. The country is home to Europe’s largest Muslim population, with more than 5 million people of the faith out of a population of about 65 million.

World leaders lined up to condemn the shooting, the deadliest attack in France since World War II, with President Francois Hollande calling it an assault of “exceptional barbarity” against journalists and a free press. U.S. President Barack Obama said in a statement that “I strongly condemn the horrific shooting.”

The newspaper devoted this week’s cover to French novelist Michel Houellebecq’s “Submission.” The novel, released Wednesday, has prompted controversy with its narrative of France in 2022 led by an Islamic party, which defeats the National Front, and a Muslim president who bans women from the workplace.

National Front leader Marine Le Pen, who features in the novel, said on France Info radio on Jan. 5 that the Houellebecq work is “fiction that could become reality one day.”

In Germany, thousands have attended anti-Islamist rallies that began in the eastern city of Dresden in October organized by a group calling itself Pegida, or Patriotic Europeans Against the Islamization of the West. The group’s rally two days ago drew its largest support yet, with 18,000 marchers.

“The Islamists, against which Pegida has warned for the last 12 weeks, have shown today in France that they’re not capable of democracy but rather rely on violence and death as a solution,” the group said on its Facebook page Wednesday. “But our politicians would have us believe the opposite.”

Karl-Heinz Kamp, academic director at the German government’s Federal Academy for Security Policy in Berlin, predicted before the attacks that any such incident would boost a group like Pegida.

“This sort of movement will explode in Germany when we have the first major Islamist violence here,” Kamp said in an interview last month. “It would grow tenfold after the first head is cut off in Cologne or Berlin.”

An estimated 200,000 refugees came to Germany last year, about 60 percent more than in 2013, according to the government, making Germany the top destination for refugees ahead of the United States. Three buildings set up to house asylum seekers were burned in Bavaria in December. Germany has about 4 million Muslims out of a population of 81 million.

In Sweden, the anti-immigration Sweden Democrats surged in elections in September, gaining 13 percent and caused a political crisis by blocking the new government’s budget. Police have investigated fires at three mosques in Sweden over the past two weeks.

“This is an event that will hardly convert anyone but it can strengthen the views of those who are already convinced,” Anders Sannerstedt, a senior political science lecturer at Lund University in southern Sweden, said of the Paris shooting.

Prince Zeid Ra’ad Al Hussein, the United Nations envoy for human rights, warned the attacks could be exploited by extremists.

“If this attack is allowed to feed discrimination and prejudice, it will be playing straight into the hands of extremists whose clear aim is to divide religions and societies,” Al Hussein said in a statement. “With xenophobia and anti-migrant sentiments already on the rise in Europe, I am very concerned that this awful, calculated act will be exploited.”

With assistance from Helene Fouquet in Paris, Leon Mangasarian in Berlin, Johan Carlstrom in Stockholm and James G. Neuger in Brussels.