Security fears intensified in Europe on Tuesday as German authorities scrambled to respond to a reported bomb plot and French investigators uncovered clues suggesting the Islamic State cell that launched last week’s devastating assaults in Paris was larger than previously known.

Authorities in Hanover, Germany, abruptly called off a friendly soccer match between Germany and the Netherlands that Chancellor Angela Merkel had planned to attend to show resolve against terrorism and support for the victims of the attacks that killed at least 129 people in Paris. One target of Friday’s attacks was a friendly soccer match between France and Germany at a crowded stadium north of Paris.

Hanover Police Chief Volker Kluwe told local broadcaster NDR that officials received “a concrete tip that an explosives attack was planned against this international match in the stadium.”

A high-level European security official said the evacuation, which was ordered shortly before the match was due to begin, was related to the Paris attacks.

Although no explosives were immediately located, the appearance of another suspected plot to wreak havoc at a crowded public event underscored the formidable challenge facing European nations as they seek to detect and prevent terrorist attacks.

In Brussels, a soccer match scheduled for Tuesday between Belgium and Spain was also canceled, and many fans expressed worry that the disruptions could threaten the European Championship in France next year.

The events in Germany took place as France unleashed a third night of intense airstrikes on Raqqa, the Islamic State’s de facto capital in Syria. French Defense Minister Jean-Yves Le Drian told TF1 television that 10 French fighter jets were launching attacks on the city. Raqqa is now the central target of the United States and allied countries seeking to dismantle the extremist group’s vast realm across Syria and Iraq.

At the same time, French authorities intensified their hunt for those responsible for Friday’s bloodshed, the worst on French soil since World War II. On Tuesday, investigators launched a search for another suspect, bringing the number of alleged attackers to nine. According to the Reuters news agency, the new suspect was detected on surveillance video in a car that the attackers used to shoot diners at cafes and bars.

Kluwe, the Hanover police chief, said the “key warning reached us about 15 minutes before the gates opened.” A senior European security official said late Tuesday that the information came from an unidentified “foreign service.” He said that investigators had not finished their work on the ground but that they did not immediately find explosives.

Authorities say as many as 20 people may have been involved in the plot to attack Paris. Here's what we know about them so far. (Gillian Brockell/The Washington Post)

German Interior Minister Thomas de Maizière said at a news conference in Berlin that the decision to cancel the match was made after “evidence solidified” during the early evening that an attack had been planned. He said that the decision to cancel the match was a “bitter” one and that “the game was a special gesture” following the Paris attacks.

The stadium threat took place the same day that two videos appeared from supporters of the Islamic State. In one video, a narrator urged Muslims to attack non-Muslim Westerners by any means possible, using cars, knives, rocks, and even kicks and punches.

“I say to European countries, we are coming,” a militant said in the other video. “We are coming with bombs and explosives; we are coming with [explosives] belts.”

French police carried out dozens of additional raids Monday and Tuesday, while investigations in France and Belgium revealed details of the attackers’ movements before the coordinated assaults. On Tuesday, France’s National Police issued an emergency bulletin appealing for witnesses to help them identify a “perpetrator” who died after detonating his explosives belt at the Stade de France on Friday. Police tweeted a photo of the dead man. The man was previously identified as Ahmad Almohammad, a 25-year-old from Idlib, based on a Syrian passport that was found near his remains.

But investigators now say the passport was fake, raising fresh questions about the man’s identity and about whether migrant trails used by asylum seekers were also exploited by militants. Officials had been unable to verify the attacker’s true identity, but fingerprints taken from the body of one of the suicide bombers match those of a man who arrived on the Greek island of Leros along with 197 migrants Oct. 3. The same man was later processed in the Serbian border town of Presevo after crossing from Macedonia on Oct. 15.

For days, a primary target of the raids has been a single fugitive, Salah Abdeslam, who is believed to be closely linked to the attacks. On Tuesday, French media reported that Abdeslam, the subject of an international manhunt, reserved two rooms at a hotel outside Paris in the days before the attacks. According to the French newsmagazine Le Point, investigators found DNA and a batch of syringes, short needles and plastic tubes in the rooms. It was not immediately clear whether the syringes were intended for explosives or drug-related use.

What we know so far about who carried out the Paris attacks

More than two months ago, ­Abdeslam — a French citizen — was stopped in a routine traffic check while entering Austria from Germany, according to a French official familiar with the investigation. He told Austrian police Sept. 9 that he was going on vacation in Vienna. There were two other people in the car, according to a spokesman for the Austrian Interior Ministry. His movements have raised questions about whether he was seeking contact with migrants — many of them asylum seekers from Syria and Iraq — along the pathways from Greece to Central Europe.

Also on France’s wanted list is Abdelhamid Abaaoud, a 28-year-old Belgian of Moroccan descent. He is suspected to be a key figure behind the Paris attacks and other terrorist operations in Europe this year, including a foiled assault aboard a high-speed train bound for Paris in August. A French official said Tuesday that Abaaoud had been targeted by French airstrikes. France began conducting strikes in Syria in September.

The United States, meanwhile, launched a strike about six weeks ago against another senior member of the Islamic State responsible for planning external attacks, Abu Mohammed al-Adnani, a U.S. defense official said. He was injured but survived the strike.

In Germany, police detained and questioned at least seven people in connection with the Paris attacks, but they were later released, the German news agency DPA reported.

In a measure of French leaders’ concern, France invoked for the first time a European Union ­mutual aid pact, known as Article 42-7 of the Lisbon Treaty, that calls for members of the bloc to assist other member states if they are attacked.

“Today, France requests the aid and assistance for all Europe,” E.U. foreign policy chief Federica Mogherini told reporters in Brussels after senior European leaders agreed to support France’s request. “And today, all of Europe, united, responds yes.”

It was not immediately clear to what extent European countries, constrained by budget pressures and divided over military action, would agree to significantly expand military action against the Islamic State. “It’s an expression of solidarity with no teeth,” said Jan Techau, director of Carnegie Europe, a Brussels-based policy research group. French President François Hollande is to meet with Russian President Vladimir Putin and President Obama next week to discuss the campaign against the Islamic State.

Remembering the victims of Friday’s attacks in Paris

Also Tuesday, Russia conducted a “significant” number of strikes on Raqqa, possibly using sea-launched cruise missiles and long-range bombers, a U.S. defense official said, speaking on the condition of anonymity to discuss the Russian operation. Those strikes follow the Russian government’s assessment that explosives brought down an airliner full of Russian tourists over Egypt last month. The Islamic State claimed responsibility for that attack.

Stephanie Kirchner in Berlin, William Branigin and Brian Murphy in Washington, Daniela Deane in London, Steven Mufson in Brussels, and Cléophée Demoustier, Virgile Demoustier, Karla Adam, Monique
El-Faizy and Karen DeYoung in Paris contributed to this report.

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