London, England (CNN) -- The attackers who planted a car bomb outside a courthouse in Northern Ireland Monday night gave only 17 minutes warning before the explosion, the Police Service of Northern Ireland told CNN Tuesday.
"It is a miracle that no one was killed or seriously injured," PSNI Chief Constable Matt Baggott said. "It is only thanks to a member of the public contacting us that we are not dealing with fatalities this morning."
The car was packed with about 250 pounds (113 kilograms) of explosives, police estimate.
A local hospital in the town of Newry got a warning call at 10:20 p.m. local time (7:20 p.m. ET) and a business was phoned two minutes later. The bomb went off at 10:37 p.m., a police representative said.
That "is not enough time to evacuate a public area," a police representative said. British police spokesmen traditionally do not identify themselves by name.
A member of the public reported a car being abandoned at about 10 p.m., she said. That appears to have given police extra time to respond.
Baggott blamed the attack on "dissident republicans," pro-Irish militants who reject the 1998 Good Friday Agreement that sharply reduced violence in the province.
Video: Bombing target symbolic
They "simply want to drag Northern Ireland back to the dark days of the past," Baggott said, condemning "cowardly attacks" by "terrorists" who "want to destroy all that is good about Northern Ireland and have no place in a modern civilized society."
"This is not an attack on a court building, this is an attack on people whose lives depend on the well-being of Newry," he added. "This is an attack that broke and damaged places of worship... damaged the ability of Newry to be at the heart of our economic success."
Newry is about 35 miles (56 kilometers) south of the provincial capital, Belfast.
Prime Minister Gordon Brown's office "strongly condemned" the bombing, saying Tuesday it was the work of a "tiny minority."
The "attack" is "entirely unrepresentative of the views of the vast majority of people in Northern Ireland," said a statement from Brown's Downing Street office.
The court building was badly damaged and businesses in the area were evacuated, police said.
Northern Ireland was wracked for decades by violence between pro-British unionists and pro-Irish republicans. About 3,000 people died in the "Troubles," as the violence was known, before the tenuous peace agreement was hammered out in 1998.
There has been sporadic violence since then. A booby-trapped car exploded on January 8, severely injuring Constable Peadar Heffron. A car bomb partly exploded outside the headquarters of the Policing Board of Northern Ireland on November 21, and another under-car booby trap exploded on October 22 in east Belfast, injuring a woman, the PSNI said.
Two soldiers and a policeman were shot dead in separate attacks in March 2009.
The two biggest parties in the province, the pro-British Democratic Unionist Party and the pro-Irish Sinn Fein, reached a deal earlier this month to bring police powers under local control, averting a crisis that had threatened to force new elections.
