The L9 Bar mines - a form of anti-tank landmine - contain explosives but need extra components to make them capable of detonating.
Assistant Chief Constable Terry Sweeney of the North-West Counter Terrorism Unit said the force's "main priority is to safely recover" the munitions that went missing from a freight train between Cumbria and Oxfordshire.
Asst Chief Con Sweeney said:
At this stage there is nothing to suggest the theft is terrorist-related, but due to the potential complexity of the investigation, our enquiries are being led by counter terrorism officers.
We would like to appeal to any members of the public who may know the whereabouts of these items, or any persons involved in the theft of these items to contact the police immediately.
I want to make it clear that, in their normal condition, these munitions are stable and do not pose a risk to the public.
However, the materials could be hazardous if they were to be tampered with and we therefore ask that anyone who sees them or knows where they are to call the police as soon as possible.
He urged anyone with any information to contact the police or Crimestoppers on 0800 555 111.
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.