Two more men have been arrested in connection with a suspected New IRA car bomb attack outside a Londonderry courthouse, bringing the total to four.
The men, aged 34 and 42 years, were arrested in the city on Sunday evening after police released footage showing the moment the car bomb exploded.
Two other men, aged in their 20s, were arrested in the early hours of Sunday morning in connection with Saturday night's "unbelievably reckless" attack.
The device exploded as police, who had received a warning, were evacuating the area. Witnesses said they heard a loud bang and saw a large plume of smoke. There are no reports of injuries.
The Police Service of Northern Ireland released four clips via Twitter on Sunday evening.
The first clip shows the Ford Fusion car, which was hijacked from a pizza delivery driver earlier that evening, being driven to the courthouse in Bishop Street.
The second clip shows a figure running away from the vehicle after parking it and the third shows a large group of young people walking past the vehicle, as well as another car driving past.
The final clip shows the dramatic moment the car exploded in a flash of light and debris being flung from the burning wreckage.
Assistant chief constable Mark Hamilton described the bomb as a "crude device" and the attack as "unbelievably reckless".
Irish Taoiseach Leo Varadkar, DUP leader Arlene Foster and Northern Ireland Secretary Karen Bradley all condemned the attack.
Ms Bradley praised politicians critical of the bombing and said the bombers will not be allowed to hold the region back.
She said: “This attempt to disrupt progress in Northern Ireland has rightly been met with utter condemnation from all parts of the community,” she said.
“The small number of people responsible have absolutely nothing to offer Northern Ireland’s future and will not prevail.
“Our voices across the political spectrum are united.
No-one has yet claimed responsibility for the attack, but Police Service of Northern Ireland Assistant Chief Constable Mark Hamilton said the New IRA was their main line of inquiry.
Two men in their 20s were arrested in the city in the early hours of Sunday by detectives investigating the explosion.
Mr Hamilton described the bomb attack as a "very significant attempt to kill people".
"Fortunately it didn't kill anybody and fortunately it didn't cause widespread damage but clearly it was a very significant attempt to kill people in the local community," he said.
He added they got everyone evacuated "just in time".
"The bomb detonated just as we were leaving the area and it is only by good grace that local people were not killed."
Mr Hamilton said the Ford Fusion used had been hijacked earlier from a pizza delivery driver by two armed men around 6pm.
"Between then and 7.23pm, a bomb was put in that car, driven at least half a mile to outside the court house on Bishop Street and around three minutes later a phone call went in to the Samaritans in West Midlands in England, which was then passed to West Midlands Police who then contacted us," he said.
More than 3,700 people died during decades of violence before the Good Friday Agreement in 1998, but uncertainty about the future of the Irish border after Brexit is reigniting tensions.
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."
Mr Hamilton described the attack as "unbelievably reckless".
Democratic Unionist Party leader Arlene Foster said it was a “pointless act of terror” which “must be condemned in the strongest terms”.
“Only hurts the people of the City. Perpetrated by people with no regard for life.
“Grateful to our emergency services for their swift actions which helped ensure there have been no fatalities or injuries," she said"
The Republic of Ireland’s Premier Leo Varadkar said his government condemns the incident in the “strongest possible terms”.
“This was an appalling, reckless and cynical act of terror,” he tweeted.
“Violence to achieve political objectives has been rejected by the people of this island again and again.”
The Taoiseach added: “I also want to acknowledge the good work and prompt response of the PSNI who prevented further harm.”
Sinn Fein Foyle MP Elisha McCallion also condemned the explosion.
“This incident has shocked the local community,” she said. “In particular, there are many elderly residents who live in the area who have been alarmed.
“Thankfully no-one appears to have been injured.
“Derry is a city moving forward and no-one wants this type of incident. It is not representative of the city.
“I would encourage anyone with information about this incident to bring it to the police.”
Local Democratic Unionist MLA Gary Middleton condemned the incident as a “disgraceful act of terrorism”.
“PSNI have confirmed there were no injuries in the serious incident at Bishops Street,” he said.
“Vehicle hijacked with explosion outside courthouse. Disgraceful act of terrorism.”
Alliance Party leader Naomi Long has also voiced her concern about the incident on Twitter, describing it as “very disturbing news”.
The incident happened just a few miles from the Irish border as the Republic of Ireland prepares to mark the 100th anniversary of its war of independence.
The Troubles began in the 1960s and led to 40 years of conflict until they were effectively brought to an end by The Belfast Agreement in 1998.