A 14-year-old boy and a 16-year-old girl have been arrested on suspicion of preparing acts for terrorism.
The boy was arrested in Blackburn, Lancashire, after police examined a number of electronic devices and raided a house in the town on Thursday.
The girl was arrested after police raided a house in Longsight, Manchester, on Friday as part of the same investigation.
Both were detained on suspicion of terrorism-related offences and bailed until 28 May. Neither has been named.
The investigation involves the north-west counter-terrorism unit, Greater Manchester police and Lancashire Constabulary.
An eyewitness to the Longsight raid quoted in the Manchester Evening News said the street was “full of terrorist police” at the time of the girl’s arrest.
The arrests are not believed to be related to the detention of nine people from Rochdale near the border between Turkey and Syria on Wednesday.
The number of terrorism-related arrests in Britain has surged in recent months as an increasing number of Britons try to travel to Syria, where they are thought to be aiming to link up with Islamic State extremists there.
