Hear Martin McGuinness and Ken Maginnis on Newsnight

Mr McGuinness said all sides, including the UK and Irish governments, had agreed to that when they signed up to the Good Friday Agreement.

It was, he said, an absolute entitlement. "If we are to be denied our position on an executive committee, then, in my opinion, it is the Ulster Unionist party breaking their word," the Mid Ulster MP said.

Ulster Unionists say Sinn Fein cannot take up posts in the executive until the IRA's have been turned over.

Mr McGuinness was speaking after Sinn Fein participated in the opening session of the Northern Ireland Assembly. The executive, which has yet to be convened, will act as the cabinet for this new government for the province.

With the assembly up-and-running the republican leadership is under growing pressure to make some sort of movement on disarmament.

Decommissioning yet to begin

Mr McGuinness is the Sinn Fein representative who has had talks with the international decommissioning body headed by Canadian General John De Chastelain.

However, there has been no sign of any movement by the republicans towards a handover of weapons.

The Fermanagh-South Tyrone MP Ken Maginnis challenged Mr McGuinness on the BBC's Newsnight on Monday to begin the decommissioning process immediately.

The Ulster Unionist MP said: "There is no one who knows more about guns and bombs than Martin McGuinness."

He added: "Can he give us some idea when in fact the first guns are going to be handed in?"

Mr McGuinness said he did not have specific responsibility to deal with IRA weapons.