Police in Northern Ireland stated on 20 January that they had detained four people suspected of involvement in a car bombing that took place in the evening of 19 January in one of the largest cities in Northern Ireland, Derry.

The Police Service of Northern Ireland has said that a security alert is currently in force in the Circular Road area in Derry after three masked men reportedly threw an object in the back of a van before abandoning it.

Security alert currently in Derry/Londonderry in Circular Rd area after report van hijacked around 11:30am by 3 masked men who threw an object in the back before abandoning it. Cordons in place. Please be patient while we work to make the scene safe. Further updates to follow. — PSNI (@PoliceServiceNI) January 21, 2019

The Northern Ireland Police Service is investigating a second security alert involving a separate hijacked vehicle in Londonderry, according to Reuters, citing a Belfast Telegraph journalist.

"Police in Derry/Londonderry dealing with 2nd security alert; Southway. Approx 1:45 pm delivery driver's vehicle was hijacked by 4 masked men, 1 of them reported to have had a gun. 2 occupants in the van ordered to drive it to Lonemoor Rd & leave it there. Cordons being put in place", police wrote on Twitter, confirming the reports.

The Police Service of Northern Ireland earlier stated they were looking into the report, but did not confirm whether there was a second incident amid its ongoing examination of a hijacked van in another part of the city.

Hijacked Royal Mail van on Creggan’s Southway. This is the second bomb alert in #Derry this afternoon pic.twitter.com/s6UoH8ivxR — Leona O'Neill (@LeonaONeill1) 21 января 2019 г.

The incident comes after a car bomb exploded in Londonderry on 19 January at around 8:10 p.m. local time (20:10 GMT). According to the Police Service of Northern Ireland (PSNI), four men were arrested in connection with what police said was an "unbelievably reckless" attack in Derry.

Detectives investigating the explosion outside Bishop Street Courthouse on Saturday 19th January have arrested a 50 year old man under the Terrorism Act. He has also been arrested in connection with an armed robbery in the Meadowbank Avenue area on Tuesday 15th January. — PSNI (@PoliceServiceNI) January 21, 2019

READ MORE: Car Explodes in Derry, Northern Ireland, Local Area on Lockdown (VIDEO, PHOTO)

Police stated that they were looking into a suspicious vehicle when they received information that a device had been left at the courthouse. It was found that the car had been hijacked from a delivery driver. No one was injured in the attack.