Derry was at the centre of new security alerts today as gangs of masked men hijacked vans in two separate attacks.

In the first case, homes were evacuated after three masked men threw an object into a van they had hijacked, then ran away.

In the second, four masked men – one reportedly with a gun – targeted a delivery van, thought to be a Royal Mail van, and ordered the driver to a specific spot before forcing him and another occupant out.

The alert comes two days after an explosion outside the courthouse in the city, which police chiefs described as “a very significant attempt to kill people in the local community”.

At 11.30am today the first trio hijacked a white Transit van in the Circular Road area of Londonderry.

Police Service of Northern Ireland (PSNI) officers closed off the road on a residential estate while they investigated, asking the public to be patient.

A community centre was used as a gathering point for residents forced to leave around 30 homes in the Creggan estate.

A controlled explosion was later carried out on the van.

Just over two hours after the first hijacking, in the same area of the city, four men with their faces covered hijacked the delivery van in Southway.

One of the gang was reported to be armed. The van’s two occupants were ordered to drive to Lonemoor Rd and leave the vehicle there. Police sealed off the area to investigate.

Saturday’s blast outside the courthouse was also in a vehicle that was hijacked by masked men. No one was injured – and detectives said it was luck that no one was killed.

Officers investigating Saturday’s explosion said today they had arrested a fifth man – a 50-year-old, who was detained under the Terrorism Act.

Four men arrested yesterday remained in police custody.

Detectives suspect dissident republican group the New IRA of being behind the explosion in Bishop Street.

Two men in their 20s were arrested in the early hours of Sunday in the city, which was a flashpoint for violence during the Troubles in the 1960s and 1970s.

Another two men, aged 34 and 42, were arrested last night.