BRUSSELS, March 24 (UPI) -- Raids across Brussels on Thursday led to the arrests of six suspects thought to be connected to the airport and subway bombings that killed 31 people and injured more than 300, prosecutors said.
Three of the arrests were made in front of the prosecutor's office in Brussels. None of the suspects were identified. Officials charges will be made on Friday.
Police are still looking for one suspect from the airport bombing and another from the subway bombing.
Another raid was made in the suburb of Schaerbeek, where residents reported a "loud bang" as police and soldiers conducted the raid, but there were no arrests.
Earlier in the day, two leaders in the Belgian government publicly expressed regret Thursday that the nation's intelligence and law enforcement communities didn't act on requests from Turkey last year to take custody of a man who's now among a group of conspirators accused in the Brussels attacks this week.
Belgian Justice Minister Koen Geens and Interior Minister Jan Jambon both said their government erred by failing to take custody of the citizen, named by Turkish officials as Ibrahim el-Bakraoui -- who police believe was one of at least four bombers in the coordinated attacks Tuesday.
"With the passing on of the information from Turkey and with the passing on of the information within Belgium, we have been slower than one could have expected under those circumstances," Geens told a news outlet Thursday. "So, the information was passed on, but we have not been diligent, or probably not diligent enough."
Jambon told a Belgian newspaper there were "two types of mistakes, at the level of the Justice Ministry and at the level of the liaison officer in Turkey, which involves the Interior and Justice ministries."
Earlier Thursday, authorities said they believe a fifth suspect was also involved in the Islamic State bombings -- two at Zaventem International Airport and one at a nearby subway station -- that killed at least 31 people and wounded hundreds more.
Investigators now believe a second attacker was involved in the train station bombing, as surveillance footage shows someone walking next to a key suspect at that location, Khalid el-Bakraoui, while holding a large bag.
Wednesday, officials said one of the suspects, Najim Laachraoui, is believed to have also been involved in the deadly attacks in Paris on Nov. 13 -- reportedly as a bomb maker.
Authorities said Laachraoui and the el-Bakraoui brothers died in the suicide attacks. The fourth suspect seen in airport footage fled the scene and is at large. It is unclear if the fifth suspect seen at the subway station died in that attack or if he is at large.
Also Thursday, NBC News cited two American officials in reporting that the el-Bakraoui brothers were already known to U.S. counter-terror officials before the bombings.
A manhunt was launched for Laachraoui last week after his DNA was found in safehouses used by suspected Paris attacker Salah Abdeslam, who said on Thursday he would not fight extradition from Belgium to France.
Abdeslam has been charged for his involvement in the Paris terror attacks but has denied knowing anything about the bombings in Belgium. Belgian broadcaster VRT reported Thursday that Abdeslam was, however, planning to participate in a larger attack, similar to what occurred in Paris.
One expert involved in tracking the Islamic State said Thursday that the el-Bakraoui brothers also hoped to build a radioactive "dirty bomb" and even spied on a nuclear researcher to that end, NBC News reported.
Officials said that of the nearly 300 people who were injured in the Brussels bombings, about 60 are in critical condition. The death toll is expected to increase.