Iain Duncan Smith is planning a shake-up of the rules on sickness benefit to encourage more people into work.
The work and pensions secretary says that the current system is too "binary" - with claimants deemed either fit or unfit for work.
Instead, claimants should be supported to take up any work they can, even if it is just a few hours, he said.
Labour says cutting benefits for people who are not able to work is punishing the disabled for government failures.
Mr Duncan Smith insisted that the "most vulnerable people in our society" will be protected under his latest reforms.
And despite the "scaremongering" of critics, he said, the UK spends more on the sick and disabled than the average of the other nations in the Organisation for Economic Co-operation and Development (OECD).
Mr Duncan Smith has also made his first public comments about revelations his department had used made-up stories from fictional sickness benefit claimants to demonstrate the positive impact of benefit sanctions.
The work and pensions secretary said the online examples were "drawn as a summary from real life cases but it wasn't a real life case".
He added: " It was quite wrong, those individuals [responsible] ultimately will face some form of disciplinary procedure."
Mr Duncan Smith's speech did not contain any policy announcements but aims instead to start a "conversation" about the next phase of welfare reform, according to DWP officials.
Mr Duncan Smith focused on the Employment Support Allowance, which is paid to those unable to work on health grounds. Those who receive the payment have their fitness to work tested under the Work Capability Assessment.
He believes those assessments should be more personalised, so if someone is able to work for a few hours they are helped to do so.
"It is right that we look at how the system supports people who are sick," he said.
Mr Duncan Smith argued what is needed is "a system focused on what a claimant can do and the support they'll need, and not just on what they can't."
He added: "Nearly 11 million adults in the UK have a common mental health condition and people are much more likely to fall out of work if they do.
"We also know that being out of work for four weeks or more can actually effect people's mental health, even if the original reason for ill health was a physical one."
'Further benefit cuts'
The shadow health secretary and Labour leadership contender Andy Burnham is set to condemn the proposals.
Speaking at a campaign rally, he's expected to say: "It's clear that Iain Duncan Smith is now preparing a new attack on disabled people".
"Talk of cutting support for people who are simply not able to work will strike fear into the hearts of many vulnerable people.
"The cruel and crude approach of the Tories has already driven many people to despair and this new drive will cause even more anxiety.
The SNPs Social Justice and Welfare Spokeswoman Eilidh Whiteford also attacked the changes being proposed, saying they would "only lead to more hardship for more people".
The MP said: "Ian Duncan Smith's speech today (Monday) is his way of trying to hide further benefit cuts and is yet another example of the Tories ideologically-driven attack on our social security system.
"There are deep seated flaws with the current assessment process. What is needed is a full independent assessment to understand the problems within the current system."