A 16-year-old youth has been arrested under terror laws by police who are also questioning a man detained at Manchester Airport.
The arrest of the teenager, from West Yorkshire, comes as police search three properties in the area.
The latest arrest and searches come after a 21-year-old man from West Yorkshire was held in Manchester on Tuesday night.
Both are being questioned in connection with terror arrests in Canada.
Security sources told the BBC the police's inquiries related to the Canadian arrests, which stemmed from an alleged al-Qaeda plot.
Following the teenager's arrest, a police spokeswoman said he "is currently being detained under the Terrorism Act 2000 and is in custody at a police station in West Yorkshire".
The 21-year-old man arrested at Manchester airport is believed to have recently been in Pakistan.
Police have confirmed armed officers were not involved in his arrest.
The operation involved West Yorkshire Police and MI5, as well as the Metropolitan Police, but is not being linked to the investigation in Forest Gate, east London.
The man, who is believed to be of Pakistani origin, is now being questioned at a West Yorkshire police station.