David Cameron faced pressure to protect disability benefits after the Government refused to rule out cuts as part of the Government's plans to slash £12 billion from the welfare bill.
The Prime Minister stressed that spending on disability benefits was higher than in the past and Work and Pensions Secretary Iain Duncan Smith insisted that the disabled would be treated with the "utmost kindness" in his welfare reforms.
In a keynote speech in Runcorn in Cheshire, Mr Cameron also signalled that ministers are prepared to make cuts to tax credits as part of the effort to balance the books.
His comments come after Chancellor George Osborne and Mr Duncan Smith confirmed plans to strip another £12 billion off the benefits bill.
Mr Cameron stressed that "w hatever the pressures, we will stand by my promises to protect the most vulnerable - including the most disabled who cannot work - because that's the sign of the compassionate country I believe in".
But asked if he would explicitly rule out any changes to disability benefits, he said: "We are actually spending more per year on disability benefits than in the past. I think that is important, helping the most disabled people."
Downing Street also failed to rule out cuts, with the Prime Minister's official spokeswoman telling reporters at Westminster: "We have said we will set out how we will deliver the £12 billion in welfare savings at the Budget and the autumn review."
In the Commons, Mr Duncan Smith refused to guarantee protection for disability benefits but insisted: "It is our purpose to protect the most vulnerable, it has been from the beginning and will continue to be so."
He added: "Our purpose is to reform welfare to get people back to work and ensure those who cannot manage and have disabilities are treated with the utmost kindness and the utmost support."
Richard Kramer, deputy chief executive at national deafblind charity Sense, said: "We would urge the Government to review its position as a matter of urgency and commit to protecting all disability benefits.
"The needs of deafblind people we support are often complex. Most deafblind people need support with communication, accessing information and mobility.
"It is important to understand that benefits such as the personal independence payment (Pip) and disability living allowance, which disabled people can receive even if they are in work, are intended to compensate for the significant additional costs of disability. For instance, a deafblind person may need to purchase expensive equipment to enable them to communicate and use a computer.
"Benefits are important for disabled people to support them to live with dignity and to lead independent lives, and are positive for society if we want disabled people to be active and part of their local community.
"We are concerned that the Prime Minister did not explicitly rule out making cuts to Pip and the other benefits that support disabled people with the extra costs of disability. It is crucial that all disability benefits, and not just the benefits that support disabled people who are not able to work, are protected in July's Budget."
In his wide-ranging speech Mr Cameron insisted that the Government was determined to tackle the root causes of inequality and not just the symptoms.
"The right track is to recognise the causes of stalled social mobility and a lack of economic opportunity," he said.
"Family breakdown. Debt. Addiction. Poor schools. Lack of skills. Unemployment. People capable of work, written off to a lifetime on benefits.
"Recognise those causes and the solutions follow. Strong families that give children the best start in life. A great education system that helps everyone get on. A welfare system that encourages work - well-paid work. These are the drivers of opportunity, and we need to extend them."
Mr Cameron highlighted three strands of his plan to improve social mobility:
:: Families will be strengthened with better childcare, flexible working and relationship support, as well as a faster adoption process and an expansion of the Troubled Families programme to help 400,000 families over the next five years
:: A focus on "first class" education, with "zero tolerance" of failing schools and a new focus on "coasting schools"
:: Creating well-paid jobs, increasing the minimum wage to £6.70 in October and the personal tax threshold to £12,500 over the next five years and "going further" as the economy recovers and welfare is reformed
Mr Cameron said he wanted to move from a society with low pay and high welfare costs to one with increased wages and a reduced benefits bill.
The Prime Minister highlighted moves to increase the income tax threshold to take people on low wages out of tax.
Mr Cameron said: " We have a system at the moment where basically we give people the minimum wage, we have tax taken from people on minimum wage and then we recycle it back to them.
"What I want to see is this move towards an economy with higher pay, lower welfare and lower taxes rather than low pay, high taxes and high welfare. That's what we should be aiming for."
Elliot Dunster, head of research, policy and public affairs at disability charity Scope, said: "In the run-up to the general election the Prime Minister vowed to 'safeguard and enhance' the value of the personal independence payment.
"But disabled people are now receiving mixed messages.
"Life costs more if you are disabled. Scope research shows that this adds up to on average £550 per month.
"Extra costs can make it extremely hard for disabled people to pay the bills.
"As speculation intensifies about where the promised £12 billion savings from the welfare budget will come from, disabled people are looking for the Government to protect the financial support they receive.
"It's critical the Government protects the value of the support disabled people receive."