"Public bickering" between the prime minister and the NHS is an "insult to taxpayers" who want clear information on health funding, MPs have said.
The House of Commons' Public Accounts Committee (PAC) criticised a dispute between Theresa May and NHS England boss Simon Stevens over finances.
Its report also censured the government for "plundering" NHS funds.
The Department of Health said the hospital sector had £1.3bn more compared with this time last year.
A spokeswoman said: "We are united behind the ambition to make the NHS the safest, highest-quality healthcare system in the world."
But Mr Stevens, who appeared before the PAC in January, contradicted these government claims.
Speaking to the committee, he said it was "stretching it" for the government to say so and that there were "substantial funding pressures".
The PAC called on both sides to work together "in the best interests of patients".
It warned that the government's "repeated raids" on NHS investment funds to meet day-to-day spending were potentially damaging.
The committee cited figures covering 2015 to 2016, when the Department of Health used £950m out of the NHS' separate £4.5bn capital budget to meet everyday running costs.
It also said that NHS England itself has "much more to do" before the public is convinced that reforms to health and care services "are not just a cover for cuts".
Last week, NHS trusts reported an £886m deficit in the last nine months of 2016.
Labour MP Meg Hillier, who chairs the committee, said: "The NHS as we know it is under threat from growing and unsustainable financial pressures."
She added: "The government seems unable to get its own house in order, plundering NHS investment funds to plug holes elsewhere."
The report made several recommendations, including:
- A "clear and transparent recovery plan" targeting NHS bodies and health economies in severe financial difficulty, by March 2017
- A report by July 2017 on how NHS finances are affecting patient care
- An end to using NHS capital budgets to meet day-to-day revenue spending, which is "not good value for the taxpayer"
- NHS England and NHS Improvement to set out how they will support the worst-performing areas and "convince the public of the benefits of the plans"
- An assessment of the impact of financial pressure on social care, by July 2017
- A report into whether there is capacity for NHS bodies to "deliver everything they are expected" to in terms of care and services, by March 2017
An NHS England spokeswoman said the PAC was right to highlight pressures and called for "fundamental agreement".
She said the NHS would "clearly set out a realistic and agreed game plan for the next two years" by the end of March.