Northern Ireland police and politicians have condemned a "reckless" car bombing outside a courthouse in the city of Londonderry.The device was placed inside a hijacked delivery vehicle and exploded on Saturday night as police, who had received a warning, were evacuating the area. There were no reports of injuries.The Police Service of Northern Ireland posted a photograph of a vehicle in flames and urged the public to stay away.Police and army bomb-disposal experts remained at the scene on Sunday.Assistant Chief Constable Mark Hamilton called the attack "incredibly reckless.""The people responsible for this attack have shown no regard for the community or local businesses," he said. "They care little about the damage to the area and the disruption they have caused."More than 3 700 people died during decades of violence before Northern Ireland's 1998 peace accord. Most militants have renounced violence, but some Irish Republican Army dissidents carry out occasional bombings and shootings.Uncertainty about the future of the Irish border after Brexit is adding to tensions in Northern Ireland.John Boyle, who is mayor of the city also known as Derry, said violence "is the past and it has to stay in the past."