Republicans must act now to sort out the mess over weapons, Mr David Trimble said tonight.
The Ulster Unionist leader, addressing party members in Co Down, said there could be no inch-by-inch negotiations in IRA disarmament.
"It is now or never. The onus is on republicans to sort out the mess they've created once and for all."
While the British and Irish governments agreed for an all-out push to restore devolution in Northern Ireland, Mr Trimble said that despite the hype there was still "no saleable deal" with republicans.
"It's clear the message hasn't penetrated through to the Republican leadership. Republicans stand in the dock and, having destroyed the trust of others, it is up to them to take steps to fix the problem. And that means action not rhetoric," he said.
He accused Sinn Fein of continued political manoeuvring against a backdrop of IRA involvement in a spy ring at Stormont, weapons training in Colombia and the break-in at a Special Branch office in Castlereagh.
"They (republicans) are the ones who broke the trust, destroyed credibility and were responsible for the suspension of the Stormont institutions."
The UUP leader said his party had "jumped" in the past to help restore devolution but this was not going to happen again.
"This time republicanism is going to have to make the first moves. The bottom line is that unionists must have certainty that republicans have become purely political and not remain paramilitary," he added.
Earlier, The Taoiseach Mr Ahern, after meeting with British Prime Minister Mr Tony Blair, said they had "charted out a work programme for the next few weeks for ourselves".
PA