Dissident republicans have admitted placing a fire bomb in a wallpaper shop in Belfast city centre.
Police have condemned those responsible
Army bomb disposal experts carried out a controlled explosion at the shop in North Street on Wednesday night.
The remains of the device were removed for further examination.
The Real IRA admitted on Thursday that it planted the device.
It used a recognised codeword in a call to a Londonderry newspaper.
Assistant Chief Constable Duncan McCausland urged traders to be vigilant and to check premises before and after trading in the run-up to Christmas.
The Lord Mayor of Belfast said the incident was "deplorable" and urged the public to defy bombers.
Alliance Party Lord Mayor Tom Ekin said: "It is clearly an attempt to destabilise the commercial life of the city
centre especially as we head towards Christmas and it has also been timed to
coincide with what is a delicate stage in the current negotiations involving the
"This does not in any way further the cause of those behind the planting of
"I would urge all city centre businesses to be vigilant but I would also say
to people not to be deterred by such incidents because the city centre is still
a good place to shop."
Michael O'Hagan, manager of the Castle Court shopping centre in Belfast city centre, said that the incident had caused quite a lot of concern.
He said: "We take it very seriously. We have our own in-house security, best practice procedures.
"It is about all the retailers being extra vigilant between now and the run-up to Christmas."
"We are refocusing on all aspects of what we would have been used to several years ago."
Mr O'Hagan said that the city centre retailers worked very closely with the police on security procedures.
He said that he did not think the alert would affect business in the city centre and assured shoppers that all security procedures were being followed.