The Conservatives' poster was based on a Guardian story
Attempts to reach a deal on elderly care in England appear to have fallen even further apart amid angry exchanges on BBC One's Politics Show.
Health Secretary Andy Burnham has called a cross-party conference on the issue after earlier talks broke down.
Lib Dem Norman Lamb backed the idea but Tory spokesman Andrew Lansley said he would only attend if Labour scrapped a £20,000 "death tax" plan.
Mr Burnham accused the Tories of making up "scare stories" about his proposals.
He said the compulsory levy on estates to pay for free personal care at home for the most elderly was just one of three options set out in a Green Paper and no decision had been reached.
He accused the Conservatives of indulging on old-style "nasty" campaigning with a "scaremongering" poster, which says: "now Gordon wants £20,000 when you die".
He added: "This is not an issue for scare stories and negative campaigning. It involves vulnerable people and we need to remember that at all times in this debate."
Mr Burnham has said he would be holding a conference involving charities and local authorities this week, to which the main political parties would be invited.
Mr Lansley was accused by Lib Dem health spokesman Norman Lamb of agreeing, during their abortive talks, that a compulsory levy was an option that had to be considered.
"Andrew's not being straight with people on this, because it was specifically recognised that there were both compulsory and voluntary options, and Andrew included that in his own draft statement of principles, and that's one of the key issues that we have to resolve," Mr Lamb told The Politics Show.
"Then it suddenly becomes the issue that results in the Tories abandoning the process and going for a very aggressive form of advertising."
He added: "I believe this has been under planning for some time and I think Andrew was genuinely trying to engage in discussion with the two of us about a really important reform.
"And I think he's been undermined by (Tory communications chief) Andy Coulson, David Cameron or whoever, and there is a divide within the Conservative Party which has prevented Andrew pursuing what was a really important attempt to build consensus."
Mr Lansley insisted this was "not true".
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After a lifetime of paying taxes our elderly deserve state-funded care. It should be paid for by reducing the benefits bill
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He said the statement the three health spokesmen had drawn up after their two meetings had set out clearly that there were "differences".
"They (Labour) wanted a compulsory levy - a death tax - and I don't," he said.
He also insisted there had been no agreement to suspend party political campaigning during the cross party talks, which he had initiated.
The Conservatives have circulated copies of a local Labour leaflet, sent on behalf of Labour's Bolton North East MP David Crausby and apparently distributed last week, which accused the Tories of scrapping the government's care plans.
But Mr Lansley admitted the "RIP" poster about Labour's plans had been based on a story in the Guardian newspaper, which had been denied by the government.
He denied it had been a pre-planned assault on the government, saying the poster had been "turned round" by Tory HQ within 24 hours of the story appearing in the newspaper.
'Lot to learn'
The Conservatives have stepped up their criticism of the government after it emerged pollsters had been employed to test the idea of a 10% tax on estates to fund elderly care.
And Shadow Education Secretary Michael Gove has also weighed in, with a personal attack on Andy Burnham.
Mr Gove, who is two years younger than the health secretary and has been an MP for less time, told BBC One's Andrew Marr programme Mr Burnham was a "young politician, idealistic, but he has a lot to learn."
The Tories have proposed a voluntary levy instead, which would guarantee free personal care.
Eighteen charities including Carers UK, the National Care Forum, Age Concern, Help the Aged, Alzheimer's Society and Macmillan Cancer Support urged the political parties not to reduce the issue to "election soundbites" and "poster slogans".
In a letter to The Times, they said: "The vexed question of who pays is unquestionably difficult, and the solutions may be controversial - but the costs of failing to act are simply too great to allow the debate needed to be drowned out by party-political squabbling."