Three security alerts in Londonderry - triggered when two vehicles were hijacked by masked men and a delivery van was abandoned - have ended.
Police said residents have been allowed to return to their homes following the alerts, which were confirmed as hoaxes.
An alert in north Belfast on Monday night has also been confirmed as a hoax.
The disruption in Derry came 48 hours after a bomb exploded in the city.
The area around the courthouse in Bishop Street, where the bomb exploded in a car on Saturday, has reopened.
The PSNI have said Saturday's bomb attack may have been carried out by dissident republican group the New IRA.
Four out of five men held over the bombing have been released.
A 50-year-old man arrested on Monday remains in police custody.
Members of the DUP are to meet Northern Ireland's chief constable on Tuesday morning to discuss recent incidents in the city and the ongoing dissident republican threat.
Police said that while the alerts were hoaxes "we cannot underestimate the impact these incidents have had on our community".
"The occupants of the hijacked vehicles did not believe when they set out for work this morning that they would be threatened by masked men," said Supt Gordon McCalmont.
"The residents in Circular Road, Southway and Northland Road did not wake up today expecting to be asked to leave their homes for their own safety.
"Too many people were affected because of the deliberate and anti-community actions of a few."
On Monday, the Army was called to two security alerts in the city involving reported hijackings.
Army bomb disposal officers carried out a controlled explosion in Creggan's Circular Road after a vehicle was hijacked by three masked men at 11:30 GMT on Monday.
The second alert on Southway, also in Creggan, followed reports of a vehicle being hijacked by four masked men at 13:45 GMT.
In a third incident, police responded to a report of an abandoned lorry on the Northland Road close to the Glenbank Road junction and St Mary's College.
In north Belfast, a controlled explosion was carried out on a suspicious object in the area of Springfield Road and Lanark Way. Residents returned to their home shortly after midnight.
St Mary's College in Derry will be open to staff and pupils on Tuesday morning.
The school principal Marie Lindsay told BBC Radio Foyle that additional support will be provided for students who may have been affected by the security alert.
A number of residents were moved from their homes. A nearby community centre was opened to people who were affected.
A spokesperson for Northern Ireland's Housing Executive said one of their vans was hijacked and that a contractor they work with has withdrawn services in the Bishop Street, Brandywell, Creggan, Rosemount and Rossville areas until further notice.
SDLP MLA Mark H Durkan said the area was largely populated by older people.
"When you see frail pensioners in their late 80s and 90s being forced to leave their homes in their dressing gowns, it really is despicable.
"There is a huge sense of anxiety right across the city, and a huge sense of anger right across the city and understandably so," he said.
What is the New IRA?
- The New IRA was formed in 2012 after a number of dissident republican organisations said they were unifying under one leadership
- It is believed to be the largest dissident republican organisation
- The group is believed to have been responsible for a number of attacks since its formation, including the murders of prison officers David Black and Adrian Ismay.
In a post on the PSNI Foyle Facebook page, police also confirmed that "there has been an attempted hijacking of a local bus service" in the Galliagh area of the city.
Saturday's bomb exploded outside the city's courthouse on Bishop Street shortly after a pizza delivery vehicle was hijacked at gun point.
A CCTV clip posted on Twitter by police showed a group of seven young people walking past the vehicle shortly before the blast.
Addressing MPs in the Commons on Monday afternoon, Prime Minister Theresa May said: "This house stands together with the people of Northern Ireland in ensuring that we never go back to the violence and terror of the past."
Northern Ireland Secretary Karen Bradley told MPs those behind the attack "will never succeed".
"Londonderry is a city that has thrived since the signing of the Good Friday Agreement 20 years ago - everyone can see that - and one that will continue to grow and develop despite the actions of those who seek to sow discord and division," she said.
DUP leader Arlene Foster tweeted that the PSNI "needs our full support to remove those responsible from our streets".
Sinn Féin councillor Kevin Campbell said there can be "no justification for this type of reckless activity".
"Those responsible for this disruption have shown complete disregard for the people of Creggan, particularly elderly people who live in this area," he said.
At the courthouse in Derry, scheduled jury trials have been put off until Wednesday.
Driver 'threatened and intimidated'
PSNI Supt Gordon McCalmont told BBC Radio Foyle the police were trying to get the city back to normal and show the attack had "little or no long-term impact".
He said the PSNI was "lucky we are not talking about loss of life".
Supt McCalmont also said the pizza delivery driver whose vehicle was hijacked and used in Saturday's bombing "had to go through the drama of having a firearm put to his head".
"He was threatened and intimidated. It would be fair to say he was asked not to raise the alarm."
He added: "These groupings obviously want us to respond. We will be very balanced. This threat has always been in this city.
"My sense is that this is not because of Brexit."