Residents have been evacuated from the Drumrallagh area of Strabane.
This follows the discovery by police of a suspect device.
Cordons are in place and traffic is being prevented from passing through the area.
This follows an incident overnight in Belfast where anti-terrorism officers disabled a viable pipe bomb.
There is not indication that the two incidents are connected.
– An earlier version of this article incorrectly stated that the suspected device was being dealt with in the Ballycolman area.
Belfast Telegraph Digital