Over the last 12 months the number of attacks on staff has doubled.

Paramedics have been threatened with knives when responding to emergency 999 calls.

On Friday, the Ambulance Service said the attacks threatened the lives of both staff and patients.

Hamper ability

Health service unions have called on politicians, community leaders and clergy to ensure that ambulance staff are able to respond to calls in every area in safety.

Ambulance Service director of operations Liam McIvor said: "This is a very serious issue as assaults of this nature can hamper our ability to quickly respond to 999 calls.

"We call upon everyone in this community to support staff and to discourage and condemn those, who by either assaults or intimidation, threaten not just our staff but the lives of patients."

At a joint news conference in Belfast, Unison official Lily Kerr said: "Ambulance staff over the past 30 years in particular have served their communities without fear or favour.

"It is somehow ironic that in the past 18 months ambulance crews are carrying out their duties with fear for their own personal safety.

"I would appeal to all political, civil and religious leaders within the community to bring all influence to bear to ensure that ambulance staff are allowed to carry out their duties in an atmosphere free from fear and violence."

'Stone cold sober'

Earlier this week, ambulance staff in Londonderry were threatened with violence if they continued to call for police back up in the city centre.

Adrian McAuley, station officer of the western division of the service, said the threat was made by two men who approached the crew of an ambulance in Derry a few weeks ago.

He said: "Two middle-aged gentlemen, who appeared to be stone cold sober, made a threat to a crew one Sunday night, along the lines of: 'You will be got, if you keep involving the RUC.'

"We took that to mean a threat to all our members, which is causing an awful lot of distress.

"They are increasingly doing their job with one eye over their shoulder."

'Crews not calling police'

Mr McAuley said the threat had followed an increasing number of violent attacks on ambulance crews in the city.