The attack happened on the Whitecross to Bessbrook Road in South Armagh this evening as the men, all textile workers, returned from a factory six miles from Bessbrook.
The mini-bus in which they were travelling was ambushed by up to a dozen attackers. It is believed the massacre was in revenge for the murders of five Catholics in Lurgan and Whitecross last night.
Initial reports suggest the passengers were forced to line up outside their vehicle, after which they were systematically gunned down.
Detectives found more than 100 spent cartridges at the scene.
One survivor remains critically ill in hospital with bullet wounds to his lungs and a further passenger, a Catholic, was ordered away before the shooting.
Nine of the dead men were from the village of Bessbrook - the bus driver came from Mount Norris.
Johnston Chapman had to identify the bodies of his two nephews, who died in the attack. He said: "They were just lying there like dogs, blood everywhere."
"If the people who did this saw them like that, surely to God if they had any conscience they would say 'well we're about to cut this out."
Both Republican and Loyalist terrorists have been involved in violence during the past few days.
The Provisional IRA has said it is ready for a full-scale military campaign if there is not a British declaration of intent to withdraw from Northern Ireland.
But the violence has been condemned from all sides.
Northern Ireland Secretary of State Merlyn Rees condemned the recent attacks as "straight gangsterism".
He said: "Retaliation breeds retaliation and unless people down there realise the wicked nonsense of what they are doing to their fellow men this will go on and on and on."
Seamus Mallon, of the nationalist SDLP (Social Democratic and Labour Party) said the barbarity of this latest crime was matched only by its cowardice.
Ulster Unionist MP Harold McCusker said he was afraid County Armagh was facing anarchy.
In Context
A commemoration service to mark the 25th anniversary of the Kingsmill Massacre, as it came to be known, was held in South Armagh in 2001.
The attack, which was one of the worst single sectarian attacks in the history of the Troubles in Northern Ireland, was carried out by a group calling itself the South Armagh Republican Action Force, which was widely believed to have been made up of IRA members.
Only one man, Alan Black, survived the attack despite being shot 18 times.
Another workman on the bus, a Catholic, was ordered away from the scene.
No-one was ever charged over the murders.