President François Hollande of France, addressing a rare joint session of Parliament in Versailles, urged lawmakers to extend for three months the state of emergency he declared after the attacks on Friday night. That designation allows the government to strip the citizenship of French natives who are convicted of terrorism and hold a second passport. Declaring that “France is at war,” he said the attacks had been “planned in Syria, organized in Belgium, perpetrated on our soil with French complicity.” He described Syria as “the biggest factory of terrorists the world has ever known,” and said France would continue the airstrikes it launched on Sunday night against Islamic State strongholds in Syria.