The PSNI confirmed a coffee jar packed with explosives had been discovered at their New Barnsley base in west Belfast. It was found before it exploded and police said it was primed to kill officers.

The "viable device" was discovered during a search following a telephone warning at 11pm on Tuesday night.

Part of the Springfield Road was closed during the subsequent alert sparked by the device.

The attack was the latest in a rash of dissident republican attempts to murder police officers this year. It prompted politicians to urge the public to be vigilant to help end the violence.

Alex Attwood of the SDLP said: "The Catholic Church made a very public and loud appeal on Monday through the media that the dissident threat required a full response from the community and they were right.

"This incident confirms it. People must respond and help police."

Chief Superintendent Gary White said: "It is appalling that in this time of progress, these attempts are still being made on officers.

"This small group of people are intent on causing disruption and mayhem within their own communities with no regard for anything other than their own selfish and callous motives."

The incident came as a top police officer was forced to withdraw from speaking at a drugs conference due to the heightened security tensions.

Assistant Chief Constable Drew Harris, of the PSNI crime operations department, had been due to address a meeting in the city centre yesterday on the fight against dealers.

Just before day two of the Association of Chief Police Officers conference, organiser Tim Hollis announced there was a security threat to members of the PSNI.

First and Deputy First Ministers Peter Robinson and Martin McGuinness met Prime Minister Gordon Brown in London yesterday after the DUP and Sinn Fein agreed arrangements for the transfer of policing and justice powers to the Stormont Assembly.

l It also emerged yesterday that Sinn Fein has been targeted by pipe bombers in Co Tyrone.

Offices in Cookstown and Councillor John McNamee were the intended victims, the party claimed.

One device near Sinn Fein offices in Burn Road appeared to have exploded and a second was discovered in Mr McNamee's neighbour's garden in nearby Arthur Street over the weekend.

See pages 10 and 11 for full coverage of the meeting with Mr Brown