Chancellor George Osborne has said he will consult with disability charities to make sure planned benefits changes are "absolutely right" as Downing Street indicated the Government is committed to pushing ahead with the controversial £1.3 billion cut.
Mr Osborne insisted the Government would "protect the most vulnerable" as he faced the prospect of a Tory backbench revolt over the plans.
But Prime Minister David Cameron's official spokeswoman stressed that reform of personal independence payments (PIP) was essential in order to curb the "ballooning" welfare bill.
Mr Osborne has come under pressure from Tory backbenchers and Labour over the planned cut, with critics claiming it is unfair to press ahead with the move at the same time as reducing taxes for the wealthy and businesses.
The Chancellor defended the Government's approach, saying: "Let me be absolutely clear: this Government will always protect the most vulnerable and help disabled people.
"That's why the disability budget is going up.
"As Iain Duncan Smith has said, we are going to make sure that it goes to those who need our help most. So in the coming months we will be talking to colleagues, to disability charities, to make sure we get this absolutely right."
Downing Street said ministers would be "engaging" with MPs and disability rights groups over the coming months before tabling legislation.
"The Government's position hasn't changed. We remain committed to making these much-needed reforms," the Prime Minister's spokeswoman said.
"We have got the time now, with the proposals out there before we bring forward the legislative proposals, to be explaining it to colleagues across the House, to be engaging with disability groups, and that's what we will do."
The intervention by No 10 came after Education Secretary Nicky Morgan appeared to indicate ministers could be open to a rethink, describing the plan as no more than a "suggestion" that is still being discussed in Government.
Jeremy Corbyn said Labour is ready to combine with Conservative rebels to inflict what would be a humiliating defeat for the Government, unless ministers back down.
The Labour leader said 200,000 of the 640,000 people hit by the changes would lose out altogether as a result of the Government's plans, which would take £4 billion out of the benefit over the course of the parliament.
He told BBC Radio 5 Live: "It is utterly appalling what they are proposing. We will be forcing a vote in Parliament on this. I hope and believe all opposition parties will join with us in that.
"I believe a number of Conservative MPs are so upset about this they too will vote against the Government."
Downing Street, however, said the changes - published last week ahead of Mr Osborne's Budget - are needed to ensure taxpayers' money is focused on those in the greatest need.
"This is about making sure that we can get PIP back to what it was originally intended to do, which was to target support on the most vulnerable and the most in need," Mr Cameron's spokeswoman said.
"Even under these proposals PIP spending will continue to rise in this parliament. This is about reining in the ballooning of this spending that we have seen over recent months."
Conservative backbencher Andrew Percy, who has organised a letter to the Chancellor calling for a U-turn, warned that the Government - which has a working majority of just 17 - faces defeat in the Commons if it tries to push through the changes.
Backbencher William Wragg became the latest Conservative to register his concern about the plan, putting his name to Mr Percy's letter and saying the "PIP changes need a rethink".
Meanwhile, disability rights groups sought to ramp up the pressure on ministers, warning there was strong public opposition to the cuts.
Rossanna Trudgian, head of campaigns at Mencap, said: "Support is being stripped away time and time again with no reassurance that the Government is working in disabled people's favour.
"People with a learning disability are being forced to the very fringes of our community due to the effects of cuts."
Robert Mooney, of the Community trade union's National League of the Blind and Disabled, said the plans were "fundamentally unfair".
"Once again, disabled people are paying the price so the Chancellor can give tax breaks to the rich," he said.
"These changes will be the straw that will break the camel's back for many of our members who face challenges in securing employment or access to health and care services."