Seven people were detained Sunday in Belgium in connection with deadly attacks in Paris as the city entered three days of mourning for the 129 people killed in the worst violence in France in decades.
   
Thousands of French troops were deployed and tourist sites stood shuttered in one of the most visited cities on Earth, while more details started to emerge about the investigation.
   
The Islamic State group claimed responsibility for Friday’s gun and bomb attacks on a stadium, a concert hall and Paris cafes that also wounded 350 people, 99 of them seriously.
   
Three of the seven suicide bombers who died in the attacks were French citizens, as was at least one of the men arrested in neighboring Belgium suspected of links to the bloodshed.
   
A French police official confirmed that a suicide attacker identified by a skin sample was living in the Paris suburbs at the time of his death. A Belgian official said two of the seven people wired with suicide vests were French men living in Brussels, and among those arrested was another French citizen living in the Belgian capital.
   
The new information highlighted growing fears of homegrown terrorism in a country that has exported more jihadis than any other in Europe. All three gunmen in the January attacks on the Charlie Hebdo newspaper and a kosher supermarket were French.
   
Authorities said three teams of attackers were involved and seven suicide bombers blew themselves up — three near the stadium and three at the concert hall and one not far from it.
   
Authorities have not said if there are more attackers at large.
   
A French police official said Sunday that three Kalashnikovs were found inside a Seat car found in Montreuil, a suburb 6 kilometers (nearly 4 miles) east of the French capital. It was one of two vehicles known to have been used in the attacks. The official, who could not be named because the investigation is ongoing, said the weapons have not yet been analyzed.
   
In Belgium, an official said the seven people detained would hear later Sunday whether they would be held in custody longer. Three other people were arrested there Saturday.
   
The official, who spoke on condition of anonymity due to the ongoing investigation, also said two of the seven attackers who died in Paris on Friday night were French men living in Brussels. He said one was living in the Molenbeek neighborhood, which is considered a focal point for religious extremism and fighters going to Syria.
   
A Brussels parking ticket had been found inside the Volkswagen Polo parked outside the Bataclan concert hall, leading investigators to one of the men ultimately arrested in Belgium, according to a French police official who spoke on condition of anonymity because the investigation was ongoing.
   
The investigation sprawled well beyond France’s borders, since Paris Prosecutor Francois Molins said some attackers mentioned Syria and Iraq.
French authorities are particularly concerned about the threat from hundreds of French Islamic radicals who have traveled 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 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 Saturday night, and they were still being questioned Sunday, the judicial official said.

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