David Cameron is standing by claims 29 district hospitals are facing cuts to emergency and maternity services.
David Cameron said 29 hospitals would suffer from cuts
The Tory leader admitted one hospital, in north-west England, had been wrongly named by him as being under threat.
But he insisted all the others were facing potential cuts. The government says reviews are being carried out.
It comes as Tory MP Henry Bellingham apologised to staff at his local hospital in King's Lynn, which he said had been wrongly included on the list.
Mr Bellingham said the Queen Elizabeth hospital should have been consulted about the campaign.
"Obviously a mistake has been made and as a local MP I wasn't consulted on this and I apologise unreservedly to the staff of the hospital," the Norfolk North West MP told the BBC.
"I do think there's a lesson for all opposition parties, all parties actually and the government, if they are issuing a statement that affects an organisation, be it a hospital, the police, some school, they should always consult the chief executive or the headmaster or whoever it is."
He later said he apologised because staff at Queen Elizabeth Hospital had felt "singled out" by being on the list when there were three other maternity units at hospitals in his constituency which were also considered under threat.
But Richard Humphreys, a spokesman for the Queen Elizabeth hospital, said: "We are not worried about other hospitals.
"We are upset that we were mentioned in the Tory report because we are not under threat."
Mr Cameron argued Queen Elizabeth hospital's maternity unit was under threat as it delivered under 3,000 live births per year - the level at which the strategic health authority decided a unit is not viable.
Another hospital, Altrincham General, named by the Tories as being under threat of losing its maternity and accident and emergency facilities does not have those departments.
Mr Cameron said the party had meant to name nearby Trafford General Hospital instead.
He admitted the error but added: "We stand by what we have in our document and we could have included many other hospitals."
Mr Cameron earlier met staff and patients at Sandwell General Hospital, which is not one of the 29 on the "at risk" list, but which the Tories say would have to absorb patients if Birmingham's City Hospital suffered cuts.
He responded to firm denials by a number of the named hospitals, including City Hospital, that units were under threat.
"It is certainly the case that at least 29 hospitals face the threat of reconfiguration or outright closure," he said.
"It's up to them to show that services are not at risk. All the examples we have drawn are taken from consultation documents."
He said patients were angry at proposed changes to district general hospitals.
"People cannot understand that cutting A&E and maternity units is progress," he said.
"People who pay their money to the NHS want to see their services saved not cut."
The government is carrying out a review of district hospitals which is likely to result in some smaller hospitals being downgraded or closed and their services moved to larger facilities.
Health minister Dawn Primarolo said any changes would be made after consultation with local people - and she accused Mr Cameron of "scaremongering".
"What David Cameron is saying is he wants to scare people in the health service - to put himself in the position of being a roadblock, regardless of what the clinical advice is," she told BBC News 24.
Sandwell and West Birmingham Hospitals NHS Trust said there was "no threat" to the accident and emergency department nor the maternity unit at City Hospital in Birmingham.
Other NHS trusts have also contradicted the Conservative claims.
The Shrewsbury & Telford Hospital NHS Trust there is no threat to maternity services at the Princess Royal Hospital in Telford.
And the Oxford Radcliffe Hospitals NHS Trust, which is responsible for Horton hospital in Banbury, said there is no threat to its A&E unit and extra consultants were being employed there.
Mr Cameron has promised a "bare knuckle fight" with Prime Minister Gordon Brown over district hospitals as he predicted it would be a key battleground at the next general election.