Reports: 2nd suspect believed in Brussels subway attack.

Belgium soldiers patrol around the main court building where Salah Abdeslam, the top suspect in last year's deadly Paris attacks, was expected to appear before a judge in Brussels, Belgium, Thursday, March 24, 2016. The Islamic State group has trained at least 400 fighters to target Europe in deadly waves of attacks, deploying interlocking terror cells like the ones that struck Brussels and Paris with orders to choose the time, place and method for maximum carnage. (AP Photo/Peter Dejong) (The Associated Press)

Map locates Brussels airport and Maelbeek metro station the locations of deadly terrorist bombings; 2c x 3 1/2 inches; 96.3 mm x 88 mm; (The Associated Press)

A police car believed to be transporting terror suspect Salah Abdeslam leaves the prison in Bruges, Belgium Thursday, March 24, 2016. Abdeslam, the chief suspect in last year's deadly Paris attacks, is facing a hearing in Brussels, amid increasing signs that the same Islamic State cell was behind attacks in both cities. (AP Photo/Geert Vanden Wijngaert) (The Associated Press)

Belgian state broadcaster RTBF and France's Le Monde are reporting that a second attacker is suspected of taking part in the bombing this week of a Brussels subway train and may be at large.

The media, citing unnamed sources, said Thursday the suspect was filmed by surveillance cameras in the Brussels metro on Tuesday carrying a large bag alongside Khalid El Bakraoui, whom prosecutors have identified as a suicide bomber. RTBF said it is not clear whether the second suspect was killed in the attack.

El Bakraoui's brother was identified as one of two suicide bombers who targeted the Brussels airport the same day in attacks that killed at least 31 people and injured more than 200.

Prosecutors did not immediately respond to the reports.