Image caption Part of Strabane was cordoned off during the security alert

A mortar bomb left near a police station in County Tyrone was a "callous attempt to kill or maim" officers, the PSNI chief constable has said.

The device was found by a resident on a wall near houses in Church View, Strabane, at 8:30 BST on Saturday.

A 33-year-old man has been arrested under terrorism legislation.

BBC News NI home affairs correspondent Julian O'Neill said: "The PSNI strongly suspects dissident republicans were behind the attempt to kill officers."

Image caption The device can be seen on a wall in Strabane as an Army robot deals with it

PSNI Chief Constable Simon Byrne tweeted it was a "stark reminder" of why the Police Service of Northern Ireland needed "7,500 officers to grow our presence in communities to deal with this severe threat".

Det Insp Andrew Hamlin said the device had been an attempt to target police officers, but that it 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," he added.

Hijacking of vehicle

A number of houses were evacuated on Saturday, but residents were allowed to return home in the early hours of Sunday after Army technical officers made the device safe.

The police are linking the incident to the hijacking of a pizza delivery driver's car in the Mount Sion area at about 21:30 BST on Friday.

A fake order was placed with a pizza outlet from a phone box on Bridge Street in the town.

When the driver arrived at the stated address, the orange-coloured Fiat Sedici was taken by a group of three men.

The car was found on fire at Evish Road, about 45 minutes later.

'Reckless, cowardly and selfish'

Sinn Féin MP Órfhlaith Begley condemned those responsible for the bomb.

"This was an attack on the entire community. Thankfully no one was injured in this disgraceful incident," she said.

SDLP MLA for West Tyrone Daniel McCrossan described those behind the bomb as "reckless, cowardly and selfish".

Image caption The wall where the bomb was found is close to the local police station and homes

"This device obviously was very sophisticated and was placed there deliberately, not only to cause a huge inconvenience but, ultimately has endangered human life," he said.

"This could have been much, much worse.

"There's no mandate for it, no-one wants it. We want them off our streets, we want them to leave and go away. That's the message that this community will be sending very strongly to those responsible."

The Police Federation chairman Mark Lindsay told the BBC's Sunday News programme: "It's a worrying development, not only for our police officers, who were obviously the target, but for members of the community.

"These devices are inherently unstable, even before they are initiated. If it was a child that came across it, we could have been looking at a fatality.

"Police officers do not feel that any sacrifice of one of them will progress things one iota, it will only be a waste of life."

On its Facebook page, PSNI Strabane thanked residents for their "support and understanding".

"To those affected by the inconvenience of having to be asked to leave your homes etc we can only apologise," the post added.

Dissident republican activity has been stepped up in recent months, with attempted bomb attacks on police in Belfast, Craigavon and Fermanagh.

Both the New IRA and Continuity IRA have been involved.