Three of the assailants in the Paris terror attack came from Brussels, three Belgian cars were involved and one suspected assailant was on the run, media reports said on Sunday.
Italian news agency Ansa and newspaper Il Messaggero said three of those involved were staying in the Brussels commune of Molenbeek, where five arrests were made on Saturday.
"The area is regarded as a cradle of radical Islamism, inhabited by a predominantly Muslim population, where many have been radicalized," Xinhua quoted Ansa news agency as saying about Molenbeek.
Meanwhile, Belgian public broadcaster RTBF said sources close to the investigation revealed that three Belgian cars were involved in Friday's attacks.
The first was a black Seat, found near Pere Lachaise cemetery in the east of the French capital. The second was a grey Polo parked near the Bataclan concert venue, which had Molenbeek parking tickets inside.
The third Belgian-registered vehicle, RTBF said, was a grey Golf which was seized by police during raids in Molenbeek on Saturday evening.
Sources told RTBF that the third vehicle could be the one used by three of those involved to return to Belgium after the attacks.
RTBF said two of the three Belgian suspects were among those arrested on Saturday, but the third remains at large -- reported to be the man who rented the grey Polo car.
RTBF said he was known to police for gang-related crime, and his brother was arrested on Saturday.
It said the authorities would not confirm the information at present as work by French investigators to identify the assailants was still on.
Ansa added that Molenbeek was already the scene of a wave of terror raids in January, immediately after the Charlie Hebdo massacre in Paris.
Also in January, police dismantled a terror cell in the southern Belgian town of Verviers, whose ringleader reportedly was also from Molenbeek.