Ken Maginnis, the Ulster Unionist Party's security spokesman, said it was "ham-fisted" of Ms Mowlam to "talk the IRA's language when she has yet to decide that the ceasefire is genuine".
He accused Ms Mowlam of "surrendering to IRA blackmail to give her the six weeks she needs to get them into the negotiations".
Peter Robinson, deputy leader of the Democratic Unionist Party, said Ms Mowlam had bought an IRA ceasefire and would constantly have to pay the price in concessions to keep it going.
"The Secretary of State has put herself in a position where she will constantly be pressured by the IRA to pay for peace," he said.
Ms Mowlam floated the idea of early releases in an interview with the Sunday Telegraph. She said she was not yet ready to discuss demands for prisoners to be released, but added: "as the ceasefire holds, other options become possible".
But a Northern Ireland Office spokesman said the Government was not yet considering the early release of terrorist prisoners. "It's an important issue and one that, as the talks process goes on, I'm sure will be up for discussion, but we're not looking at it now," he said.
The early release and transfer of political prisoners forms a key part of the "introductory document" presented to Ms Mowlam by Gerry Adams, the Sinn Fein president, when they met for preliminary talks at Stormont last week.
Sinn Fein wants the immediate return to Ireland of 20 prisoners held in jails in England and then the release of them and others. Early releases were made after the last ceasefire by reintroducing a policy of 50 per cent remission, which had been abandoned some years before. That level of remission remains.
Ms Mowlam will decide at the end of the month whether the IRA ceasefire is genuine, and whether Sinn Fein will be invited to join the multi-party talks on the future of Northern Ireland on September 15.
Meanwhile, nationalists marched yesterday to mark the 26th anniversary of internment, the policy of imprisonment of suspects without trial, less than 24 hours after loyalists clashed with police at the end of the annual Apprentice Boys' parade in Londonderry.Reuse content