Counter terrorism officers are investigating after firearms, chemicals and other suspicious items were found in Dewsbury and Liversedge.
A 42-year-old man was arrested yesterday (Monday) following the search of a property in Halifax Road.
A number of chemicals were found at the address.
He was arrested on suspicion of conspiracy to produce class A drugs and offences under the explosives act.
Another property in Penn Drive, Liversedge, has also been searched as part of the investigation.
Chemicals, suspected firearms and other suspicious items were found, which are now being examined by officers.
A 43-year-old man from Liversedge has been arrested on suspicion of conspiracy to produce class A drugs, offences under the explosives act and firearms offences.
Both men are still in custody.
Search teams are still at both addresses.
The North East Counter Terrorism Unit is leading the investigation supported by West Yorkshire Police.
Supt Julie Sykes, from Kirklees Division, said: “We recognise that local people may have concerns as a result of this activity and would like to reassure them that the property is not believed to present any risk to local residents.
“During searches at the property, public safety has remained the priority of investigating officers. To ensure the best possible protection, specialist officers will continually assess the situation. If at any point the material is believed to present a risk to local people, the necessary safety measures will be activated immediately. However, at no stage has this property been a risk to surrounding residents.
“I am grateful for the patience and understanding of people locally.”