Alert follows explosion at Crawford Square in Derry
An explosion which damaged a probation office in Londonderry was caught on CCTV
Police said they were given an "inadequate" warning before the device went off.
The blast was reported to the police at about 22:55 BST on Monday. There are no reports of injuries.
Army bomb disposal experts examined the scene of the explosion, after the device was left at the door of a probation office in Crawford Square.
Some residents were moved from their homes but have since returned after a police cordon was lifted.
The head of the Probation Board Cheryl Lamont has said that security measures will now be reviewed.
"My understanding from police is that actually there is very limited damage that's restricted to some scorch damage on the front door.
"We hope that later this afternoon some staff will be over and we'll look at that to make sure its fit for staff to use.
"We're always very mindful of security but certainly I will be, with my senior colleagues, reviewing security."
There were concerns that a second device had been left but Supt Mark McEwan said he was confident the area was now clear.
"Basically a warning was given that was totally inadequate in terms of allowing the police to actually take any positive action and the device activated before police were able to start the evacuation.
"We have to condemn outright the very fact that somebody has put a bomb in a highly residential area here and that has been placed here in order to intimidate, cause damage and potentially cause serious injury or death."
Bernie Webster, who lives in Crawford Square, said residents were in an extreme state of panic.
"We heard the bang as we were getting ready for bed and we headed straight out into the street," she said.
"There was very quickly chaos developing because the explosion was very close to a house with young children in it.
"They were out in the street in their pyjamas with their mother and were absolutely hysterical.
"A few of the neighbours brought them into one of the houses and tried to get them calmed down. It was a dreadful situation, it really was.
"We had an English visitor staying with us last night and we feel totally humiliated by what has happened in the last 24 hours."
Cheryl Lamont, the acting director of the Probation Board for Northern Board, said the attack caused risk to members of the public.
"We appreciate the messages of support from partners, politicians and local groups which we are extremely grateful for and we can reassure the public we will continue to work to make local communities safer."
The nearby Methodist Mission has over 40 residents. Its director Liam Milligan told BBC Radio Foyle that it was a senseless attack.
"I just can't understand the logic of someone that would carry this out," he said.
"We wish to condemn this attack in the strongest possible terms. Those who carried it out demonstrate a complete disregard for human life and the safety of residents living in the Crawford Square area.
"Families with young children live in the immediate vicinity of the attack and it is extremely fortunate we are not reporting serious injury or loss of life.
"Our sympathy and support go to the families who had to leave their homes," he added.