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At least 127 are dead and dozens more are wounded after gunmen and bombers attacked a concert venue, the Stade de France sports stadium, and nightlife spots around Paris on Friday night.
Speaking in a televised address to the nation on Saturday, French President Francois Hollande called the attacks an "act of war" and vowed to "act by all means anywhere, inside or outside the country" to "triumph over the barbarism."
Former president Nicolas Sarkozy added in a statement: "The war we must wage should be total."
According to news outlets, the Islamic State (ISIS) has released a statement claiming responsibility for the attacks and threatening further attacks against France. The group reportedly said the killings were in response to airstrikes against its militants, adding France would remain a "key target."
France is a member of the U.S.-led coalition waging airstrikes against ISIS fighters in Syria and Iraq; the country launched its first airstrikes in Syria in late September.
During a meeting with a delegation of French lawmakers in Damascus on Saturday, Syrian President Bashar al-Assad said France's "mistaken policies... had contributed to the spread of terrorism."
The attacks in Paris come just days after suicide bombings in Beirut killed more than 40.
Responding to the attacks on Twitter, The Intercept's Murtaza Hussain noted that "these things are all connected."
A state of emergency, declared by Hollande on Friday evening, remains in place on Saturday. Hollande also declared three days of national mourning.
France 24 reports that the French government has banned public demonstrations in Paris and the surrounding area until Thursday, with Paris police chief Michel Cadot saying authorities cannot "provide security for specific marches or gatherings."
The Guardian is live-blogging developments here. France 24 is doing so here. The BBC's live feed is here.