Stormont Castle in Belfast has been evacuated following the discovery of a letter bomb.
The bomb was addressed to Northern Ireland Secretary Theresa Villiers, who is also the Conservative MP for Chipping Barnet.
The castle houses the offices of Northern Ireland's First Minister Peter Robinson, of the Democratic Unionist Party, and Deputy First Minister Martin McGuiness, of Sinn Fein.
Ms Villiers was not at Stormont Castle when the letter bomb was found - she is in London meeting US diplomat Richard Haass.
It is believed the letter bomb was from dissident Irish republicans, and their actions have been condemned.
It is the fourth such device to be intercepted in Northern Ireland since Friday.
Responding to Tuesday's incident, Mrs Villiers said: "I utterly condemn the attempted attacks we've seen over recent days.
"If those responsible think that this kind of criminal activity will further any agenda, then they are completely mistaken."
Northern Ireland's First Minister Peter Robinson condemned those who sent the letter bomb.
"Those responsible for sending this, and other devices, through the post have absolutely no regard for the lives of postal workers and staff working in offices," he said.
"They will not further any aim or objective by their vile and callous deeds. Northern Ireland will not be dragged back by terrorists who have nothing but misery to offer."
Bomb found at Stormont Castle in Belfast
Stormont Castle in east Belfast was evacuated during the alert
A letter bomb addressed to Northern Ireland Secretary of State Theresa Villiers has been made safe by the British Army at Stormont Castle in east Belfast.
The castle houses the offices of Northern Ireland's First minister and Deputy first minister.
Staff were evacuated after the package was found in the postroom of the building on Tuesday morning.
It is the fourth such device to be intercepted in Northern Ireland since Friday.
Dissident republicans have been blamed for sending them.
Northern Ireland Secretary Theresa Villiers
No Surrender To The IRA: It is believed Irish republican thugs sent the letter bomb to Mrs Villiers
Two were addressed to police officers and the other was sent to the offices of the Public Prosecution Service in Londonderry.
Ms Villiers was not at Stormont Castle when the letter bomb was found - she is in London meeting US diplomat Richard Haass.
Responding to Tuesday's incident, she said: "I utterly condemn the attempted attacks we've seen over recent days.
"If those responsible think that this kind of criminal activity will further any agenda, then they are completely mistaken."
'Vile and callous'
First Minister Peter Robinson moved to Parliament Buildings during the alert, while Deputy First Minister Martin McGuinness was not in the castle.
Mr Robinson condemned those who sent the letter bomb.
"Those responsible for sending this, and other devices, through the post have absolutely no regard for the lives of postal workers and staff working in offices," he said.
"They will not further any aim or objective by their vile and callous deeds. Northern Ireland will not be dragged back by terrorists who have nothing but misery to offer."
Justice Minister David Ford said: "This is yet a further attempt to attack a public figure.
"Do those sending these devices really think their intended target will personally open the package? Their actions are to be condemned by all right-thinking people."
BBC News - Bomb found at Stormont Castle in Belfast
The bomb was addressed to Northern Ireland Secretary Theresa Villiers, who is also the Conservative MP for Chipping Barnet.
The castle houses the offices of Northern Ireland's First Minister Peter Robinson, of the Democratic Unionist Party, and Deputy First Minister Martin McGuiness, of Sinn Fein.
Ms Villiers was not at Stormont Castle when the letter bomb was found - she is in London meeting US diplomat Richard Haass.
It is believed the letter bomb was from dissident Irish republicans, and their actions have been condemned.
It is the fourth such device to be intercepted in Northern Ireland since Friday.
Responding to Tuesday's incident, Mrs Villiers said: "I utterly condemn the attempted attacks we've seen over recent days.
"If those responsible think that this kind of criminal activity will further any agenda, then they are completely mistaken."
Northern Ireland's First Minister Peter Robinson condemned those who sent the letter bomb.
"Those responsible for sending this, and other devices, through the post have absolutely no regard for the lives of postal workers and staff working in offices," he said.
"They will not further any aim or objective by their vile and callous deeds. Northern Ireland will not be dragged back by terrorists who have nothing but misery to offer."
Bomb found at Stormont Castle in Belfast

Stormont Castle in east Belfast was evacuated during the alert
A letter bomb addressed to Northern Ireland Secretary of State Theresa Villiers has been made safe by the British Army at Stormont Castle in east Belfast.
The castle houses the offices of Northern Ireland's First minister and Deputy first minister.
Staff were evacuated after the package was found in the postroom of the building on Tuesday morning.
It is the fourth such device to be intercepted in Northern Ireland since Friday.
Dissident republicans have been blamed for sending them.

Northern Ireland Secretary Theresa Villiers

No Surrender To The IRA: It is believed Irish republican thugs sent the letter bomb to Mrs Villiers
Two were addressed to police officers and the other was sent to the offices of the Public Prosecution Service in Londonderry.
Ms Villiers was not at Stormont Castle when the letter bomb was found - she is in London meeting US diplomat Richard Haass.
Responding to Tuesday's incident, she said: "I utterly condemn the attempted attacks we've seen over recent days.
"If those responsible think that this kind of criminal activity will further any agenda, then they are completely mistaken."
'Vile and callous'
First Minister Peter Robinson moved to Parliament Buildings during the alert, while Deputy First Minister Martin McGuinness was not in the castle.
Mr Robinson condemned those who sent the letter bomb.
"Those responsible for sending this, and other devices, through the post have absolutely no regard for the lives of postal workers and staff working in offices," he said.
"They will not further any aim or objective by their vile and callous deeds. Northern Ireland will not be dragged back by terrorists who have nothing but misery to offer."
Justice Minister David Ford said: "This is yet a further attempt to attack a public figure.
"Do those sending these devices really think their intended target will personally open the package? Their actions are to be condemned by all right-thinking people."
BBC News - Bomb found at Stormont Castle in Belfast
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