Vehicle checkpoints are to return to Belfast after a bomb partially exploded in the city centre yesterday.
The number of police patrols will also increase after the device was left in a vehicle at the Victoria Square shopping centre car park.
The car's terrified driver was forced to transport the 132lb (60kg) of explosives after masked men in boilersuits hijacked his vehicle in North Belfast on Sunday night.
Police Service of Northern Ireland (PSNI) Chief Superintendent Alan McCrum said: "We are all aware of the threat that is posed by terrorists.
"Everyone can play a part in helping to tackle this by remaining vigilant and by reporting any suspicious activity."
A US State Department spokeswoman condemned the recent "cowardly" acts of violence and pledged continued support for those who are working to build a stronger society, a vibrant economy and an enduring peace.
"The vast majority of the people of Northern Ireland are committed to the peace process and to living in a society free of the violence and hatred of the past," she said.
"Over the past 15 years, the people and institutions of Northern Ireland have made great progress toward peace, stability and prosperity.
"Those intent on violence will not deny Northern Ireland the opportunity to fulfil these goals."