The North-West Counter Terrorism Unit (NWCTU) has launched an appeal for information after munitions were stolen from a freight train between Cumbria and Oxfordshire.
Ten packages - each containing four separate plastic cases - were initially reported missing to the British Transport Police shortly after 7.30am on Thursday, after the train arrived at Didcot, Oxfordshire, a Greater Manchester Police spokesperson said.
Seven packages were found near a railway line in the Folley Lane area of Warrington, Cheshire.
However, three of the packages - made up of a total of 12 plastic cases - are still missing.
Police enquiries are ongoing, the spokesperson said.
The Ministry of Defence-owned munitions were believed to have been taken off the train while it was temporarily stationary in Warrington, and seven of the packages were discarded nearby.
More top news
Aaron Ramsey struck seconds after Diego Costa's equaliser to win the FA Cup for Arsenal at Wembley against 10 man Chelsea.
Passengers have been told not to travel to Heathrow and Gatwick because of "extreme congestion" after all BA flights were cancelled.
A band of heavy, thundery showers continues to move northwards through this evening, dying away overnight.