A 33-year-old man remained in custody last night being questioned by detectives investigating an attempt to kill police officers in Strabane.
An improvised explosive device was discovered by a local resident in Church View in Co Tyrone town on Saturday morning. It is thought to have been placed there the night before.
The object was examined by police and Army Technical Officers and was found to be a viable mortar style device.
Officers from a nearby police station are thought to have been the intended target.
Several residents had to leave their homes while the mortar was made safe and removed for forensic examination.
A car believed to be used by the bombers was hijacked from a pizza deliver driver in the Mount Sion area of Strabane at around 9.40pm on Friday.
The orange Fiat Sedici was taken from the driver by three men and was discovered on fire at Evish Road around 45 minutes later.
A 33-year-old man was arrested on Saturday and is being questioned by detectives from the serious crime squad.
It is the sixth attempt to kill police this year.
Last month a bomb exploded close to the Fermanagh border after officers were lured to the scene with a hoax call. No one was injured in the attack at Wattlebridge.
In July a similar attempt to lure officers took place in Craigavon with a hoax bomb with a secondary device attached.
Both attacks were claimed by the Continuity IRA.
Senior Police Service of Northern Ireland commander Superintendent Gordon McCalmont said the seventh attack this year in Strabane was cause for concern.
He warned: "It is designed to kill and harm people."
Mr McCalmont added: "For some reason it has failed to deploy. It could have went anywhere.
"It was stored and sitting overnight for eight or nine hours in this vulnerable position where a member of the public found it."
Detective Inspector Andrew Hamlin said the mortar "had the capacity to kill or seriously injure anyone in the vicinity".
"This is not the first time a deadly device has been left in a public space recently and serves to remind us all how little the terrorists responsible care for the lives of local people.
"I am keen to hear from anyone who saw the orange Fiat in the town or who noticed anything out of the ordinary in the Church View area on Friday night"
PSNI Chief Constable Simon Byrne tweeted it was a "stark reminder" of why the PSNI needed "7,500 officers to grow our presence in communities to deal with this severe threat".
SDLP MLA Daniel McCrossan said "residents could have been killed".
"There is no place for these criminals on the streets of our town," he said.
"Thanks to the residents who discovered the device and the actions of police we aren't dealing with a tragedy this morning."
Sinn Féin MLA Órfhlaith Begley said: "Those behind this alert have nothing to offer the people of Strabane and have no support.
"These actions need to end immediately."
Chair of the Police Federation, Mark Lindsay, said mortars attacks were "notoriously indiscriminate and inaccurate".
"Members of the public were just as likely to have borne the brunt of this savagery as our colleagues," he said.
"What this thwarted attack tells us is that these terrorists are determined to kill – and to kill anyone, not just police officers. They are setting lethal traps with murderous intent and are clearly in search of what they disgustedly call a 'spectacular'.
"They want to show some warped relevance through their brutal and sickening attacks and on the vicious assaults they commit within communities who want to see the back of them."
