Chief Superintendent Harry Breen and Superintendent Bob Buchanan are the most senior policemen to be killed since the troubles began.

They were returning from a meeting with the Gardai Siochana in the Irish Republic where they had been discussing a range of issues including ways of combating IRA attacks on the cross-border rail link.

The officers left a police station at Dundalk, Republic of Ireland, at about 1500 GMT and turned off the main Dublin-to-Belfast road, taking a detour outside the town back to Northern Ireland.

There are unconfirmed reports the men were travelling out of uniform in an unmarked, private vehicle, without protection, but for security reasons there were several routes open to them.

As they approached a country border crossing outside the small village of Jonesborough, County Armagh, along Edenappa Road, gunmen, lying in wait for them behind a wall, opened fire.

The IRA's South Armagh brigade said it had ambushed the men after monitoring their movements and would issue a more detailed statement later.

Leak

Although the RUC held regular Monday meetings they did not normally include Mr Breen, leading to suggestions the IRA kept a close watch on the station or received inside information.

Security sources are dismissing claims of a leak because only senior Gardai officers would have been aware of the officers' presence at the meeting.

But it would have been easy to tail the car, belonging to Mr Buchanan as it had Northern Irish number plates.

An army helicopter has been surveying the area but troops will not recover the bodies until tomorrow morning.

There are fears the area maybe booby trapped, with bombs concealed in derelict buildings at the scene of the murders.

A total of 260 police officers have been killed in 28 years of violence, 38 of them in South Armagh.

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