UUP leader Mr David Trimble tonight said the absence of actual decommissioning in a manner which would maximise public confidence meant there was "nothing at present for Ulster Unionists to respond to."
"There are moreover matters in the Government's proposals such as amnesty to which we take the strongest exception."
Earlier today, Mr Trimble said: "We're glad to see that the IRA has taken a significant step towards decommissioning but it hasn't actually begun decommissioning. "And of course we want to see that happen."
He added: "However, it leaves open a number of issues, the most important of which is ensuring there is actually a process and that the process begins."
Mr Trimble is due to brief his assembly party and peers tomorrow.
Meanwhile, SDLP leader Mr John Hume said he "welcomed today’s statement from the IICD in respect of the initiation of a process that will put arms completely and verifiably beyond use."
"We look forward to IICD reports of further significant developments and want to see all armed groups make real progress on decommissioning through the IICD."