David Duchovny co-starred in The X-Files

The film will see David Duchovny and Gillian Anderson reprise their famous roles as alien-hunting FBI agents Mulder and Scully.

Series creator Chris Carter will direct the as-yet unnamed film when production begins in Vancouver, Canada.

The first X Files feature film was released in 1998 as a spin-off to the successful cult TV series.

Fox also announced the sequel will be released on 25 July 2008 in the US.

'Supernatural thriller'

The script, written by Chris Carter and Frank Spotnitz - who also co-wrote the first X-Files movie - is being kept a close secret.

All that is being revealed is that it is a "supernatural thriller" and will develop the complicated relationship between Mulder and Scully.

The original cult series was a hit when it ran from 1993-2002, winning three Golden Globes for best TV drama.