In terms of the weaponry, in terms of technical ability, it is a very real threat

Stephen White Assistant Chief Constable

A number of armed and masked men also hijacked a lorry in the area.

It was subsequently set on fire and blocked the main A1 Newry to Dundalk Road.

Newry and Armagh assembly member Danny Kennedy, of the Ulster Unionist Party, has blamed dissident republicans on the bomb.

The disruption came as the North-South Ministerial Council, set up under the Good Friday Agreement, met in Dublin.

Cross-border rail services have been severely disrupted by security alerts in the past.

At one stage, a cross-border rail link was closed for six days, following reports of explosions near Newry.

Assistant Chief Constable Stephen White, who was in charge of the operation, said the threat from the Real IRA should not be underestimated.

"In terms of the weaponry, in terms of technical ability and technical expertise, it is a very real threat," he said.

"The numbers may not be as large as the Provisional republican terrorist movement.

"But certainly in relation to the threat, it is very real."

Opposed

About 40 miles of track between Portadown, County Armagh, and Dundalk was affected.

The security forces later found three other possible blast sites. However, no devices were found.

Up until February this year, there had been 32 major security alerts between Belfast and Dublin.

Last June, an explosion damaged the Belfast to Dublin railway line a few miles from Newry.

The dissident republican Real IRA was blamed for that attack.

Dissident republicans are opposed to the 1998 political accord and the Northern Ireland peace process.