The assassination of a prison officer on his way to work has been described in the House of Commons as a "dastardly act"
The officer was shot dead when he was ambushed on a motorway on his way to work on a stretch of the M1 between Portadown and Lurgan, Co Armagh.
The man is the 30th prison officer killed in Northern Ireland since 1974.
The shooting happened at around 7.30am, at the same time as a major security alert further along the motorway at a shopping centre at Sprucefield, near Lisburn, where bomb disposal experts were called in to check a car.
Paul Girvan, a Democratic Unionist Party (DUP) member of the Northern Ireland Assembly, said the man was on his way to begin duty at the top-security Maghaberry Prison, near Lisburn, Co Antrim, where dissident republicans have been involved in long-running protests against jail conditions.
It is believed this vehicle might have been linked in some way to the shooting, according to some sources.
The DUP's Westminster leader Nigel Dodds told the House: "Today's dastardly news of the murder of a prison officer by terrorists in Northern Ireland reminds the entire House that the battle against terrorism and for democracy and for freedom still continues in Northern Ireland."
North Antrim's DUP MP Ian Paisley called for Ms Villiers to make a statement to the Commons on the security situation in Northern Ireland.
He said MPs would be "in equal measure saddened and outraged" by the shooting.
Commons Leader Andrew Lansley told him: "The House does indeed share your sense of shock and outrage in relation to that death."