Police officers in Derry have examined three abandoned vehicles in the area in less than 24 hours, just days after a car bomb exploded outside a courthouse in the Northern Irish city.

The Police Service of Northern Ireland (PSNI) took to its Foyle Facebook page on Monday evening to warn residents that they were examining a vehicle at Northland Road.

"Please avoid the area at this time," a spokesperson said.

Elderly residents were evacuated from their homes in pyjamas as police attempted to secure the area.

Earlier on Monday the PSNI carried out a controlled explosion on a van that was hijacked by three masked men and examined a Royal Mail postal van that was hijacked by another group of four men.

No one was injured in Saturday's blast, but the incident highlighted the threat still posed by militant groups in Derry.

A 50-year-old man was arrested on Monday in relation to Saturday's attack and detained under the Terrorism Act, police said.

The first four men arrested hours after the attack have all been released unconditionally.

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Officers evacuated homes and cordoned off residential areas as they inspected the abandoned vehicles on Monday.

Derry was rocked by violence during the Troubles throughout the 1960s and 1970s and Saturday's car bomb has been condemned across Northern Ireland's political divide.