Police in Northern Ireland (PSNI) are investigating three separate incidents of vehicle hijackings in Derry/Londonderry on Monday, following a weekend of violence in the city.
The first incident took place mid-morning on Monday when three masked men hijacked and later abandoned a transit van, the PSNI said on Twitter.
The masked group threw an object into the back of the van before abandoning it, a witness told Reuters.
Police later carried out a controlled explosion on the van.
A second incident was reported several hours later after four masked men hijacked a delivery vehicle and abandoned the van.
"One of [the men] was reported to have a gun," the PSNI said.
It is not yet clear whether the two incidents are connected.
Later on Monday, police said they were investigating a suspicious object in north Belfast and closed roads as a precaution.
The incidents come after a weekend of violence in Derry/Londonderry, where an explosive-laden car was detonated outside the local courthouse on Saturday night.
No injuries were reported.
UK Prime Minister Theresa May condemned the weekend car bomb attack in a statement in parliament on Monday.
"I'm sure the whole House will join me in condemning Saturday's car bomb attack in Londonderry and paying tribute to the bravery of the Nothern Ireland police and the local community," she said.