BRUSSELS — The French authorities have concluded that Abdul Hamid a 27-year-old Belgian who has fought in Syria for the Islamic State, was the mastermind of the Paris terror attacks.A French official briefed on the investigation, who spoke on the condition of anonymity because he was not authorized to discuss operational details, said that Mr. Abaaoud — already a suspect in a Belgian terrorist plot that was foiled in January — had mentioned plans to attack “a concert hall” to a French citizen who returned from Syria. Mr. Abaaoud, this official said, was also in contact with Ismaël Omar Mostefaï, one of the Paris attackers.President François Hollande of France said the attacks had been “planned in Syria, organized in Belgium, perpetrated on our soil with French complicity” and described Syria as “the biggest factory of terrorists the world has ever known.”
Mr. Hollande reiterated his determination to annihilate the Islamic State. “France is at war,” he told a rare joint session of Parliament at the Château de Versailles. Mr. Hollande proposed extending the state of emergency that he declared on Friday for three months, and making it easier to revoke the French citizenship of those who hold dual passports and are involved in terrorism.The United States has given support to the French airstrikes on the Islamic State stronghold in Raqqa, Syria, but President Obama on Monday again ruled out a ground intervention. “Let’s assume that we were to send 50,000 troops into Syria,” he said at a gathering of leaders of the Group of 20 industrial and emerging-market economies in Antalya, Turkey. “What happens when there’s a terrorist attack generated from Yemen? Do we then send troops into there? Or Libya, perhaps?”
Across France and Belgium, the authorities raced to track down suspects and chase leads.French officials conducted police raids around the country overnight, detaining 23 people.aIn Belgium, heavily armed police officers wearing balaclavas descended on neighbourhoood in Brussels early Monday in an unsuccessful search for Salah Abdeslam, 26, who is believed to have helped .The raid nded after more than three hours. Mr. Abdeslam remains at large. His brother Ibrahim was one of the attackers who died in Paris. A third brother, Mohamed, and four other men who had been detained were released on Monday.