-- Deadly terrorist attacks in Brussels on Tuesday have prompted Belgium's national soccer team to cancel its scheduled practice session.
Multiple explosions rocked the Brussels airport and subway system Tuesday morning, forcing a lockdown of the Belgian capital and heightened security across Europe. At least 31 people were reported dead.
The Royal Belgian Football Federation posted an announcement on the Twitter account for its national team, saying, "Football is not important today" and that "our thoughts are with the victims."
Belgium will host Portugal in a friendly match on March 29 at the King Baudouin Stadium in Brussels. The game is scheduled as a warm-up for both teams ahead of this year's European Championship in France.
The Portuguese soccer federation said it was in contact with Belgian authorities about security arrangements for the match.
French Interior Minister Bernard Cazeneuve said the explosions are a reminder that a "very high security level" will be required during the European Championship. He said the measures taken to guarantee "collective security" at the June 10-July 10 tournament will include the mobilization of specially trained emergency staff, police forces and firefighters.
The Islamic State group claimed responsibility for the attacks, saying in a posting from the group's Amaq news agency that its extremists opened fire in the airport and "several of them" detonated suicide belts. It also said that another suicide attacker struck in the subway. The posting claimed the attack was in response to Belgium's support of the international coalition arrayed against the group.
"What we feared has happened," Prime Minister Charles Michel told reporters. "In this time of tragedy, this black moment for our country, I appeal to everyone to remain calm but also to show solidarity."
There were two explosions in the departure hall of the city's Zaventem international airport, according to Michel. About an hour later, another bomb exploded on a rush-hour subway train near the European Union headquarters. Terrified passengers had to evacuate through darkened tunnels to safety.
Brussels Mayor Yvan Mayeur said 20 people were killed and more than 100 were injured in the train explosion. Belgian media initially reported at least 13 dead in the airport explosions but later decreased that number to 11, citing information from Belgian Health Minister Maggie de Block, who also said 81 people were injured.
"Prayers & thoughts go to all families and friends of the victims," Belgium midfielder Axel Witsel posted on his Twitter account.
One international soccer player was at the Zaventem airport when the explosions were reported. Norwich forward Dieumerci Mbokani, who is from Congo, was "unharmed but shaken by the tragic events," the English club said in a statement.
Mbokani was visiting family in Brussels, where he played for Anderlecht for two seasons until 2013.
Belgian golfer Thomas Pieters lives in Antwerp, Belgium, and is playing at the WGC-Dell Match Play Championship in Austin, Texas.
"I woke up at 6 a.m. and my phone was just buzzing,'' Pieters told ESPN. "Everybody was asking me, is your family okay. And I kind of knew what was going on so I opened the news sites and it was just one of the worst days to wake up. Even when it happened in Paris, it's close, but it's not right near your people. And then now it happens to somewhere I go almost every time I fly out. That's where I go. It's shocking to see so many images and the videos. It's a sad day.''
The explosions occurred four days after Salah Abdeslam, a prime suspect in the Nov. 13 Paris attacks that killed 130 people, was arrested in Brussels.
ESPN FC, ABC News and The Associated Press contributed to this report.