A controlled explosion was carried out on a suspicious object with shopping in on a busy Saturday badly disrupted.
Mr Donaldson said the object was a viable device.
Part of the city centre was closed to traffic in the security alert at Market Place.
The road was closed between Smithfield Street and Chapel Hill as Army Technical Officers carried out the controlled explosion.
Mr Donaldson said: “I condemn those responsible for this bomb incident on a busy saturday afternoon in a packed city centre. This caused major disruption and incovenience for shoppers and local businesses alike.
“It is not clear who or what was the target but the people who did this have no support in our local community. I commend the PSNI and the ATO for their action in safeguarding the public from harm.”
Police and ATO later carried out an operation in the Lagmore area of West Belfast after they tracked down a car in which they believe a viable device fell from in Lisburn.