French President François Hollande announced Friday that his country had entered a "state of emergency" with a mobilized military and tightened borders.
"This is an attack not just on Paris. It's an attack not just on the people of France. But this is an attack on all of humanity and the universal values we share," he said.
While the U.S. president said "we're going to do whatever it takes to work with the French people and with nations around the world to bring these terrorists to justice," he stressed that his office did not yet know all the details of the attacks, so the U.S. would not speculate who may have been behind the attack.
"This is a heart-breaking situation, and obviously those of us here in the United States know what it's like. We've gone through these kinds of episodes ourselves, and whenever these kinds of attacks happen, we've always been able to count on the French people to stand with us," Obama said. "They have been an extraordinary counter-terrorism partner, and we intend to bear with them in that same fashion."
Hollande delivered remarks soon after Obama, saying his country has "mobilized all the possible forces for neutralization of terrorists," according to a translation from his official Twitter account.
Hollande also announced that the "state of emergency will be declared and the borders will be closed," and he called for his nation to "show unity and cold blood."
It was not immediately clear how quickly France could close its borders, since — as a European Union country — it maintains an open system. France's foreign ministry announced later Friday that, despite the heightened security, flights and trains would continue.
For its part, Belgium said it would impose new checks on the French frontier, and air and rail arrivals.
About 140 people were killed Friday in 7 separate attacks — shootings and explosions among them— around Paris, police and news outlets said.
A police official said 11 people were killed in a Paris restaurant in the 10th arrondissement, and others said at least twice that number died elsewhere, primarily in the Bataclan concert hall, where the hostages were taken. It was unclear how many people were in the hall; one official said there were around 100 while another said there were far fewer.
Hollande later announced that he would not participate in the G20 meeting in Turkey this weekend. The official Twitter account of the French presidency tweeted that Hollande would bring together a council of defense meeting Saturday morning at 9 local time.
Paris agencies announced Friday that all metro stations had been closed in the city, and all schools and universities in the region would be closed on Saturday.
U.S. Secretary of State John Kerry said Friday evening that the American embassy in Paris is making every effort to account for U.S. citizens after the attacks.
German Chancellor Angela Merkel said Friday evening that she was deeply distressed by the news and images from Paris, and that her thoughts were with the victims.
Other European officials were quick to comment on the incident, with European Council President Donald Tusk tweeting that he was shocked by the attacks, and he offers his "full solidarity & sympathy with the French people and authorities."
Other international leaders were quick to follow:
— Reuters and The Associated Press contributed to this report.