Derry bomb attack an attempt to kill police officers
No one was injured in the blast at Crawford Square which occurred shortly before 11.00pm.
One street in the Square remains sealed off as police continue to examine a second suspect device.
Twenty families who had been evacuated remain out of their homes.
Northland Road, which had been sealed off, has been reopened.
The bomb had been left at the door of a probation office which sustained blast damage.
A car parked nearby was set on fire.
The attack has been condemned by local MLAs.
Colum Eastwood, of the SDLP, said The Samaritans had received a call that a device had been left in the area and when police arrived it exploded.
Speaking to Derry Now at the scene this morning, Mr Eastwood said the attack was “morally wrong.”
He said: “This is an attack in the middle of a residential area and probably intended to kill police officers and could easily have killed anyone.
“These type of activities are morally wrong, they are futile and they will get us absolutely nowhare.”
Sinn Fein MLA Raymond McCartney also condemned the attack.
He said: "Thankfully, no one was injured as a result of this reckless attack in a built-up residential area.
"This has brought nothing but disruption to the lives of local people and to the city generally with the closure Northland Road, one of the main arterial routes in the city.
"This is a city moving forward and the people have made it clear that they do not want these type of incidents."
He concluded: "We will not allow a tiny minority to drag us back to the past."