Image caption 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 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.

Two were addressed to police officers and the other was sent to the offices of the Public Prosecution Service in Londonderry.

Police have confirmed that the device found on Tuesday was similar to the others.

Later on Tuesday, senior Northern Ireland police officers warned a committee of MPs at Westminster that dissidents remained firmly wedded to violence.

Assistant Chief Constable Drew Harris told the Northern Ireland Affairs Committee: "There does not seem to be any diminution in their intent or any sense of them trying to find some route for dialogue with other parties or the government.

"They seem entirely wedded to a route of violence."

He added: "We have concerns about upcoming anniversaries and whether they want to use those for their own purposes in getting publicity."

Chief Constable Matt Baggott told committee members that intensive investigative efforts would go into finding the letter bombers.

'Part of the job'

Media playback is unsupported on your device Media caption Secretary of State Theresa Villiers condemned the letter bomb

Ms Villiers was not at Stormont Castle when the letter bomb was found - she was in London meeting US diplomat Richard Haass.

Responding to Tuesday's incident, she said facing terror threats was "sadly still a part of the job".

She added: "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."