The area surrounding Peter Robinson's office was sealed off

It was discovered at the East Belfast MP's constituency office at Belmont Avenue in the city on Monday.

A second device was sent to the SDLP's Alex Attwood at the Policing Board's offices in Clarendon Docks in Belfast.

Army bomb experts were called and the devices were taken away for forensic examination.

Mr Robinson said it was an attempt to kill or injure him and his office staff.

"It's an attempt by those who do not have a mandate to intimidate those who do have a mandate," he said.

"They will not move me or my colleagues one iota from the path that we are going to go forward on by this kind of attack."

Security Minister Ian Pearson described the attacks as an "affront to democracy".

"These incidents are direct attacks on the democratic process and they only make us more determined in our resolve to see a complete and permanent end to all paramilitary activity," he said.

"The security forces will continue to bear down on the activities of all paramilitary groups and I would urge anyone with information regarding these incidents to contact the police."

The Alliance Party's assembly member for East Belfast, Naomi Long, said the attacks were "reckless".