Police are keen to trace the woman, pictured from CCTV footage (BRITISH TRANSPORT POLICE)

Police are hunting a woman after a teenage girl was sexually assaulted while on a train.

The British Transport Police have released a CCTV image of the woman they want to trace in connection with the assault, which took place on board a train from London to Milton Keynes.

The incident happened on Monday August 19, between 7.15pm and 8pm.

The woman was last seen exiting Milton Keynes Station (GETTY)

The woman is said to have squeezed a teenage girl’s thighs a number of times.

A official statement read: “British Transport Police are today releasing a CCTV image after a sexual assault on board a train from London Euston to Milton Keynes.

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“The incident happened between 7.15pm and 8pm on Monday 19 August.

“A woman is reported to have touched a teenage girl’s thigh a number of times.

“The woman then left the train at Milton Keynes.

(BRITISH TRANSPORT POLICE)

“Officers believe the woman in the image may have information that could help their investigation.”

Anyone who knows the woman pictured is asked to contact BTP by texting 61016 or by calling 0800 40 50 40m quoting reference number 1900071882, or by calling Crimestoppers anonymously by calling 0800 555 111.