Deadly terrorist attacks in Brussels on Tuesday have prompted the Belgium national soccer team to cancel its scheduled training 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 28 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 was scheduled to face Portugal in a friendly on March 29.

At least one of the attacks was likely the result of a suicide bomber, the Belgian federal prosecutor reported. He classified the attacks as the work of terrorists.

There were two explosions in the departure hall of the city's Zaventem international airport, according to Prime Minister Charles Michel. There was also an explosion on the rail tracks at the Maelbeek subway station, according to a spokeswoman for Brussels transportation department. Fifteen people were killed in the subway station and 13 at the airport, officials said.

Belgian transportation officials also confirmed that an additional 55 others were injured at the subway blast, including 10 people in critical condition.

There was no immediate claim of responsibility for Tuesday's attacks, and Belgian Prime Minister Charles Michel said there was no immediate evidence linking key Paris suspect Salah Abdeslam to them. The explosions happened four days after Abdeslam, a prime suspect in the Nov. 13 Paris attacks that killed 130 people, was arrested in Brussels.

"What we feared has happened," 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."

ESPN FC, ABC News and The Associated Press contributed to this report.