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Police have released four men who were arrested as part of an investigation into the attempted murder of two officers in Strabane, County Tyrone.

The officers had been on patrol in the town when a bomb detonated at the side of their vehicle on Thursday.

Neither officer was injured in the explosion, which happened before 23:00 GMT in the Mount Carmel Heights area.

Three men - two aged 36 and one aged 28 - were arrested on Friday and then another man, aged 38, on Saturday.

They have all been released following questioning and the investigation continues, police said.

Detectives have previously said that a strong line of inquiry was that dissident republican group the New IRA was behind the attack.

The incident caused a major security alert, which affected more than 1,000 residents and left some children unable to get to school.

Police said they found what could be a command wire for an improvised explosive device during follow-up searches.

PSNI (Police Service of Northern Ireland) Assistant Chief Constable Bobby Singleton said officers had been conducting routine patrols into anti-social behaviour in the area and were left shaken when they saw a flash and heard a loud bang.

The attack was widely condemned, with Sinn Féin deputy leader Michelle O'Neill describing it as "reprehensible and reckless".

Democratic Unionist Party (DUP) leader Jeffrey Donaldson said it was clear those responsible offered "nothing but hurt and disruption for the communities they purport to represent".