Detectives are appealing for witnesses following a security alert in the University Road area of south Belfast on Friday 20th June.
Detective Chief Inspector McCallum said: “At approximately 10.10pm, police received a report that an object had been thrown through a window of the building and a device had been left inside.
“Ammunition Technical Officers attended and determined the device to be viable.
“A 34-year-old man was arrested at the scene under the Terrorism Act, he remains in police custody at this time.
“I am appealing to anyone who may have witnessed the incident or to anyone with CCTV or other footage that could assist with the investigation to contact detectives.
“I am also keen to speak to a passer-by, believed to be a young man, possibly in his 20s, who bravely intervened on the night and assisted in apprehending the suspect until police arrived.
“Detectives from the Serious Crime Branch continue to work to establish a motive for this attack and are exploring a number of potential motivating factors including the possibility that this is a hate crime.
“At this time, no other persons are being sought in connection.
“Anyone with any information is asked to contact us on 101, quoting reference number 1808 20/06/25.”
A report can be submitted online using the non-emergency reporting form via http://www.psni.police.uk/makeareport/ or you can also contact Crimestoppers anonymously on 0800 555 111 or online at http://crimestoppers-uk.org/