One man remained in custody late on Monday following the discovery of an explosive device and the attempted hijacking of a car in Derry.
Three other men arrested under the Terrorism Act were released from custody.
Police are linking the discovery of the device near a playing field to the attempted hijacking of a delivery driver’s vehicle by three masked men armed with knives and a gun at Hollymount Park on Friday night.
They ran off towards the Corrody Road close to where a device was found on Saturday. It was close to a sports pitch where children were playing Gaelic football and described as viable by police.
Three men, aged 54, 32 and 29, were released on Monday. A 34-year-old remained in custody.
Derry City and Strabane commander, Chief Superintendent Nigel Goddard, said the explosive device had been "recklessly left in a public area".
"[It was] just metres away from houses and a sports area where a number of children were playing football," the senior police officer said.
"Our focus remains firmly on keeping people safe against the threat posed by violent groups.
“No matter what level of involvement people have with any criminal or terrorist activity, we will investigate and where appropriate, put people before the courts to answer for their actions."
Sinn Féin councillor Christopher Jackson said the area was popular with residents, including dog walkers.
"There is a lot of anger from residents, who would use this area to go and clear their head," he told BBC Newsline.
"There is also a lot of anger from from parents of young children who were playing a Gaelic competition here."
Dissident republicans, including the so-called New IRA and an even smaller splinter group, have been active in recent months, particularly in the north west.
Two police officers escaped injury when a device was detonated beside their police vehicle in Strabane, Co Tyrone.
