Pressure is mounting on Sinn Fein after a report the IRA had been secretly buying weapons while publicly decommissioning.
A senior Ulster Unionist MP said the position of Sinn Fein ministers in the power-sharing Northern Ireland Executive was untenable.
In a British newspaper report, IRA chiefs are said to have bought a consignment of high powered new Russian special forces rifles in Moscow late last year.
The purchase is believed to have taken place some time between their first act of decommissioning and their second recent destruction of what was described as a substantial amount of ammunition, guns and explosives.
The Russian security services are said to have detected the deal and passed details to British military intelligence in London, according to the Sunday Telegraph.
The report comes on the top of police revealing that they had discovered what was called an "IRA hit list" of top Tory politicians.
At the same time, a top republican in Co Tyrone was last night still being questioned about the murder of a Catholic taxi driver near Dungannon on Wednesday night.
Ulster Unionist MP Jeffrey Donaldson said he had been briefed on the Russian arms affair and if accurate it meant the IRA was "in clear breach of the Good Friday Agreement".
He said: "I think the Government and the other parties have to urgently consider the position of Sinn Fein/IRA and their role in the Northern Ireland Executive."