French president Francois Hollande evacuated from Stade de France

— -- French president Francois Hollande was evacuated from the Stade de France during France's friendly match against Germany on Friday after two loud explosions were heard outside the ground during the first half.

The explosions took place around 15 minutes into the game, which continued until its conclusion. A police official confirmed one explosion in a bar near the stadium. It is unclear whether there were casualties there.

The explosions were part of the worst terrorist attacks on France in its history. French police say at least 40 were killed in multiple acts of violence, including shootings at restaurants and a hostage-taking at a music theater. France authorities announced the country has closed its borders -- the first time it ever has done that.

A Paris police official also said there were at least 100 hostages in a Paris theater

"Those that think they can terrorize people in France or the values that they stand for are wrong," President Barack Obama said in comments late Friday afternoon from the White House.

After the match, which France won 2-0, supporters were gradually allowed to leave the Stade de France in small groups. In addition, thousands of fans waited on the pitch at the end of the game as reports of the violence flowed in.

A stadium announcer made an announcement over the loudspeaker after the match, telling fans to avoid certain exits "due to events outside,'' without elaborating. At first that prompted some panic, but then the crowds just walked dazed, hugging each other and looking at their phones for the latest news of the violence. All postgame interviews with players were canceled.

Having been evacuated, Hollande immediately went to the Interior Ministry to follow the response to the attacks.

Sirens were immediately heard, and a helicopter was circling overhead.

Earlier in the day, the German team had to evacuate their hotel because of a bomb threat, but police found no explosive devices.

U.S. Homeland Security Department officials monitoring the attacks in Paris say there is no known, credible threat against the United States.

In a statement, NFL spokesman Brian McCarthy said of the league's heightened NFL security measures: "Security at our games is always at a heightened state of alert."

The attack comes as France has heightened security measures ahead of a major global climate conference that starts in two weeks, out of fear of violent protests and potential terrorist attacks.

France has been on edge since deadly attacks by Islamic extremists in January on satirical newspaper Charlie Hebdo and a kosher grocery that left 20 dead, including the three attackers. The restaurant targeted Friday, Le Carillon, is in the same general neighborhood as the Charlie Hebdo offices. The country has seen several smaller-scale attacks or attempts since, including an incident on a high-speed train in August in which American travelers thwarted a heavily armed Islamic radical trying to attack passengers.

Information from The Associated Press was used in this report.