Four people have been arrested by police on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism in Syria
Two men aged 29 and 18 both from Levenshulme, and a 21-year-old woman from Trafford are in custody, Greater Manchester Police said.
A 29-year-old man from Oxford has been arrested by the South East Counter Terrorism Unit on suspicion of the same offence.
Police said a number of properties were now being searched as part of the investigation.
More top news
Jessica Urbano Ramirez was two weeks away from her 13th birthday when she died in the June 14 blaze.
No-one was on board the single-decker vehicle, Humberside Police said.
The disgraced film producer has been the subject of an investigation in the US into allegations that he sexually assaulted numerous women.