Health Secretary Jeremy Hunt has been accused of taking part in a "deliberate, planned, co-ordinated and cynical" attempt by the Conservatives to damage the reputation of the NHS in Wales.
Mr Hunt told the House of Commons earlier this week that care failures in Wales were increasing pressure on casualty departments in England, with a 10% rise in Welsh patients using A&E services in hospitals on the English side of the border since 2010.
He claimed health authorities in Labour-controlled Wales acted as if the lessons of the inquiry into the Mid Staffordshire tragedy, in which hundreds more people died than expected, "stop at the border".
But Welsh health minister Mark Drakeford said the numbers of English patients using Welsh casualty departments had also grown by 10% over the same period, which had seen average attendances at A&E rise by 11% across the country.
Accusations that NHS standards were much lower in Wales than in England were "simply not true", said Mr Drakeford, describing Mr Hunt's suggestion that Welsh patients were flocking over the border to escape poor treatment in Wales as "absolutely absurd".
Mr Drakeford told BBC Radio 4's Today programme: "We have a long and porous border. Numbers are up everywhere."
Mr Hunt's claims were "not to do with facts at all" but were "part of the deliberate, planned, co-ordinated and cynical attempt by the London Conservative Party to drag the reputation of the Welsh NHS through the mud", he said.
Mr Drakeford added: "Are there things we could do better? Of course there are. Are there days when the Welsh NHS is under strain? Of course it is. But it is equally true on the other side of our border too.
"The accusation that Welsh patients die in Welsh hospitals at levels which demand a national inquiry is certainly not the case."