Two Brussels brothers known to police were among the suicide bombers who carried out deadly attacks on the international airport and subway in the Belgian capital, local media reported Wednesday, while an arrest was said to have been made during a raid.
An official confirmation was not immediately available. Federal prosecutors have scheduled a press conference for 1 pm (1200 GMT).
The Brussels brothers, Khalid and Brahim El Bakraoui had been involved in organized crime, but had so far not been linked to terrorist activities, police sources told the broadcaster RTBF.
It had first reported that the two brothers had blown themselves up at the Brussels airport, but later joined other Belgian media in saying that the brothers had split, with one targeting the airport and the other the Maelbeek subway station.
The attacks are believed to have killed some 31 people, while nearly 260 were injured, Health Minister Maggie De Block told the broadcaster Radio 1. Those figures could still change, she added.
The Islamic State jihadist group has claimed responsibility for both attacks in Brussels.
Khalid El Bakraoui had used a false identity to rent an apartment in the Brussels neighbourhood of Forest where a shootout with police occurred during a terrorism raid last week, RTBF said. That incident later led to the arrest of Paris attack suspect Salah Abdeslam.
The 27-year-old El Bakraoui is also thought to have rented a hideout in the southern city of Charleroi that was used to prepare the deadly terrorist attacks in Paris last November, the broadcaster said.
He had been sentenced in early 2011 to five years in prison for carjackings, after having been arrested in possession of Kalashnikov rifles, according to the Belga news agency.
Khalid El Bakraoui carried out the bombing at the Maelbeek station, which is believed to have taken place in a subway train, RTBF said.
His brother, 30-year-old Brahim, had been sentenced in 2010 to nine years in prison for having shot at police with a Kalashnikov rifle during a hold-up, Belga said. He was one of the suicide bombers at the airport, according to RTBF.
The broadcaster also reported that another Brussels airport suspect whom police have been looking for since Tuesday may be Najim Laachraoui, an accomplice of Abdeslam who had been sought for months in connection with the Paris attacks.
The newspaper La Libre Belgique and the broadcaster RTL reported Wednesday that Laachraoui was arrested during police raids in the Brussels neighbourhood of Anderlecht. Other Belgian media said they could not confirm this information.
According to some media reports, Laachraoui may also be a man that police have been looking for in connection with the Brussels attacks. That suspect's suicide bomb is believed not to have exploded at the airport.
The three suspects arrived at the airport by taxi, the mayor of the nearby town of Zaventem told the news agency. The taxi driver gave police the address where he picked up the three men, according to the broadcaster VTM.
While international rail service was slowly returning to normal, the airport - Belgium's hub for international flights - remained closed on Wednesday.
"Because the forensic investigation is still underway, we currently have no access to the building. It is therefore impossible for us to assess the damage. As a result the airport will remain closed to air traffic today," Brussels Airport said in a statement.
"In the course of Wednesday we will assess when the operations can be resumed," it added.
Some 1,500 to 1,600 stranded passengers spent the night in three emergency shelters, Belga wrote.
The Maelbeek station is expected to remain closed for weeks, the news agency quoted Brussels mayor Yvan Mayeur as saying.
Belgian Prime Minister Charles Michel is expected to go to the station together with his visiting French counterpart, Manuel Valls, on Wednesday at 12 pm (1100 GMT). Brussels authorities have called for a minute of silence at that time.
Belgian King Philippe and Queen Mathilde are also scheduled to mark the minute of silence near the Maelbeek station.
Churches across the country have been asked to ring their bells after the minute of silence, as a sign of "a deep sorrow and at the same time hope," the Belgian bishops' conference said in a statement.
Belgium is in the midst of holding three days of national mourning. The public has been laying out flowers and candles in a central square since Tuesday.
An emergency meeting of European ministers responsible for security could be convened as early as Thursday on Belgium's request, Dutch Security and Justice Minister Ard van der Steur said on Twitter.