Two days after a car bomb exploded in Derry, Northern Ireland police carried out a controlled explosion on a hijacked vehicle. A second abandoned van was being examined.
There was a large bang and black smoke from the first van after an army bomb disposal robot entered. Police said the van had been hijacked by three masked men who threw an object in the back before abandoning it on a residential street.
A Royal Mail postal van was hijacked nearby later on Monday (local time) by four masked men, one of them reported to have a gun, police said. Officers evacuated a number of homes and cordoned off the area as they inspected the vehicle.
No one was injured in the blast on Saturday outside a court but the incident highlighted the threat still posed by militant groups opposed to a 1998 peace deal that largely ended three decades of violence in the British-run province.
Saturday's blast came at a time when police in Northern Ireland and European Union member Ireland have warned that a return to a hard border between the two after Brexit, complete with customs and other checks, could be a target for militants.
ATO have carried out a controlled explosion on the hijacked vehicle in the Circular Road area of Derry/Londonderry.— PSNI DC&S District (@PSNIDCSDistrict) January 21, 2019
A number of homes remain evacuated and cordons remain.
We continue to ask the public for their patience, and thank them for their co-operation.
However, neither Britain's Northern Ireland minister Karen Bradley nor the Police Service of Northern Ireland (PSNI) said they saw any links between Brexit and the incidents in the province's second largest city, that lies close to the border with Ireland.
"We are not picking up any information that indicates that anybody wants to engage in violence in relation to the Brexit issue, certainly not at this point," PSNI Assistant Chief Constable Mark Hamilton told Irish broadcaster RTE.
Bradley said the threat level in Northern Ireland would remain at "severe," where it has stood since 2009 when two British soldiers and a policeman were killed in the worst attacks in the province for over a decade.
"Although there has been a reduction in the overall number of national security attacks in recent years, vigilance in the face of this continuing threat remains essential," she told Britain's parliament in London.
A fifth man was arrested on Monday in relation to Saturday's attack. The 50 year old was detained under the Terrorism Act while four other men remained in custody, police said.
There were no details from police on who may have been behind the hijackings in Derry.
Four men, aged 42,34 and two aged 21, arrested by detectives investigating the explosion at Bishop Street in Derry/Londonderry on Saturday 19 January, have been released unconditionally. A 50 year old man arrested earlier today remains in police custody— PSNI (@PoliceServiceNI) January 21, 2019
The main focus of the car bomb investigation is the New IRA - one of a small number of groups opposed to the 1998 Good Friday agreement.
This mostly ended a conflict between mainly Protestant unionists who want Northern Ireland to remain part of the United Kingdom and predominantly Catholic nationalists, who want a united Ireland, in which some 3600 people had died.
The group was formed in 2012 after three of the four main militant nationalist groups merged. It was the first time since the peace deal that most of the disparate nationalist groups still intent on violence had come together under one leadership.
"It's an organisation that has evolved over recent years," the PSNI's Hamilton said.
"They are a smallish grouping and they have a different presence in different parts of the province but, they remain committed to the aims of the violent dissident republican groups that we know exist here."