Twin teenage girls who are thought to have travelled to Syria are "deeply religious Muslims", police understand.
It is understood an older brother has joined the extremist militant group Islamic State of Iraq and the Levant (Isis), and one line of inquiry is that the girls may have flown out to join him.
The girls, from a large Somalian family, flew from Manchester International Airport to Turkey which borders Syria where the civil war involving Muslim militants is raging.
Greater Manchester Police said the pair had been in contact with relatives since their departure.
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The Grammy-winning singer posted a picture of the two on his Instagram saying the two got engaged right before the new year.
British Airways said it was taking the matter "extremely seriously" and is assisting police with their enquiries.
The rest of this weekend will see further spells of rain or snow across the UK. Icy roads expected