Greater Manchester Police is due to hold a news conference at 12:10pm.
It is expected that further details will be revealed of an arrest made in connection with an offensive Facebook page set up following the deaths of PC Fiona Bone and PC Nicola Hughes.
More top news
The postal services company 'apologised for the inconvenience' after delivering the postcard, which was dated 1966.
Man who has barricaded himself in house for three days may have a stash of petrol and other explosives, police say.
Jessica Drake is the 11th woman to allege Donald Trump engaged in inappropriate sexual behaviour.