NICE, FRANCE >> The Latest on a truck that drove into the crowd in Nice (all times local):
German police say they're stepping up border checks on the French frontier following the attack in Nice.
Federal police said Thursday that they had increased checks at land borders and railway crossings with France, and at airports.
They would not give further details, but said the move was made in consultation with France.
The children's hospital in Nice says it has treated some 50 children and adolescents injured in the truck attack, including two who died during or after surgery.
Stephanie Simpson, the communications director for the Lenval foundation hospital, tells The Associated Press that injuries included fractures and head injuries and that the victims were aged 18 or under.
In a phone interview, she said: "Some are still life and death."
She said she could not say exact number of children hospitalized or the ages of those who died.
The hospital is also offering psychological counselling to parents and siblings.
The hospital, equipped with one of France's largest pediadiatric emergency units, also called the families of children it was already treating before the attack to ask them to pick up their children to free up rooms for the attack victims.
French Prime Minister Manuel Valls said the government is declaring three days of national mourning after the attack in Nice that left at least 84 people dead. Speaking after an emergency meeting, Valls said the national mourning would begin Saturday.
He confirmed that a measure extending the country's state of emergency would go before lawmakers next week.
Valls and French President Francois Hollande were going to Nice later Friday.
French Foreign Minister Jean-Marc Ayrault has cut short a visit to Mongolia to return to Paris because of the Nice attack.
A foreign ministry spokesman says Ayrault was in Mongolia for the Asia-Europe summit and is expected back late Friday.
Germany's top security official says the attack in Nice is "incomprehensible and simply awful," and that "this barbaric murder must be finally brought to an end."
Interior Minister Thomas de Maiziere said Friday he was shocked by the news of the attack and that his thoughts were with the victims and their family.
De Maiziere says "our friendship with the French people will become even deeper in mourning, anger and determination."
Belgium's prime minister said he's convening a meeting of the National Security Council Friday in the wake of the Nice attack, to make sure adequate security measures are in place for Belgium's national holiday next week.
"We have already taken a certain number of steps in connection with preparations for July 21, as you can imagine, and our security services are permanently evaluating the measures that are necessary," Charles Michel, the Belgian prime minister, said in a radio interview. "It's certain that our security services are going to include information resulting from this act committed last night in Nice in their analyses."
On March 22, suicide bombers killed 32 victims in the Brussels Airport and subway. The Belgian capital was also home to many of the attackers who killed 130 people in Paris on Nov. 13.
Both of those attacks were claimed by the Islamic State group.
A lawmaker for the region that includes Nice said some people tried to escape the attack by going into the sea, giving new details of the horrifying last minutes of the attack in Nice.
"A person jumped onto the truck to try to stop it," Eric Ciotti told Europe 1 radio. "It's at that moment that the police were able to neutralize this terrorist. I won't forget the look of this policewoman who intercepted the killer."
Christian Estrosi, the regional president in Nice, said some of the city's 1,200 security cameras had pinpointed the moment the attacker boarded the truck, far from the seaside "in the hills of Nice" and could follow his path to the promenade. Estrosi called for the investigation to focus on any accomplices.
"Attacks aren't prepared alone. Attacks are prepared with accomplices," Estrosi said. "There is a chain of complicity. I expect it to be unveiled, discovered and kept up to date."
Estrosi said more than 10 children were among the dead and he said France needed to think carefully about its next response to attacks, as previous responses were not enough to protect the people.
Russian news agencies on Friday quoted Irina Tyurina, spokeswoman for the Russian Union of Travel Industry, saying that a Russian woman was killed and her friend hurt in the Nice attack. Tyurina said she got the information from insurance agencies.
"Two friends from Russia were taking a walk on the Promenade des Anglais. One was killed by the truck, the other lightly injured, she's got broken toes and some other minor injuries," Tyurina said.
Thousands of Russian tourists are estimated to be holidaymaking in Nice.
Tour de France riders including race leader Chris Froome sent messages of support to the victims of the deadly attack in Nice, although organizers did not immediately say whether cycling's showpiece event will continue as planned.
Froome posted a picture of the blue, white and red French flag on Twitter and wrote: "Thoughts are with those affected by the horrific terror attack in Nice."
The city of Marseille has canceled its fireworks show on Friday. The seaside city, not far from Nice and one of France's largest, announced the cancellation after an attack on Nice's waterfront promenade left at least 84 people dead.
The French Interior Ministry has raised the death toll to 84 from the attack on people celebrating Bastille Day in the Riviera city of Nice. The additional four deaths were apparently from the 18 people who were seriously injured when a truck slammed into the crowds. Minister Bernard Cazeneuve said extra medical-legal police were being sent to Nice to speed the identification process so bodies can be returned to families.
France, hit with two waves of attacks last year that killed 147 people, has long known it is a top target for the Islamic State group. In September 2014, then-spokesman Abu Mohammed al-Adnani referred to "the filthy French" in a statement telling Muslims within the country to attack them in any way they could, including "crush them with your car."
The message was not limited to France. It addressed "disbelieving Americans or Europeans — especially the spiteful and filthy French — or an Australian or a Canadian."
This corrects an earlier version to say that Ayrault was at Asia-Europe summit