Care homes may have unknowingly received coronavirus patients from NHS hospitals early in the crisis, an NHS boss has suggested, as another said such facilities have been "neglected for too long".
The prime minister claimed the government had "a system of testing people going into care homes" and that testing was being "ramped up".
Following the row in PMQs, NHS Providers CEO Chris Hopson issued a statement denying NHS Trusts were "systematically discharging" patients into care homes.
"Trusts deeply resent this suggestion," he said.
"It is categorically not true to say that NHS trusts have been systematically discharging patients they know or suspected had Covid-19 into care homes."
However, the statement also admits that capacity issues meant tests could not be carried out consistently on all patients going into care homes until "mid-April".
Mr Hopson said: "It is only since mid-April that sufficient testing has been available to conduct these tests sufficiently.
"It was only therefore only on April 15 that trusts were asked to systematically test every single patient due for discharge to social care."
In the Commons, Labour leader Sir Keir quoted a cardiologist, who said: "We discharged known, suspected and unknown cases into care homes which were unprepared with no formal warning that patients were infected, no testing available and no PPE to prevent transmission.
"We actively seeded this into the very population that was most vulnerable."
The prime minister's spokesman said ministers are "doing whatever it takes to resolve the situation" in care homes.
"We’ve been working since beginning of the outbreak to seek to minimise the rate of infection in care homes and the spread of the disease," the spokesman said.
That includes 116 mobile coronavirus testing units across the country which are able to test residents and staff in-situ.
He added how more than £1 billion had been made available to help the care sector since the crisis began.
Following criticism of the government's care home response, Prime Minister Johnson pledged £600 million to help care homes with coronavirus "infection control".
The cash will be handed to councils and ring-fenced for care homes, ITV News Political Corresponded Paul Brand said, and homes will be able to spend it on infection control.
Responding to the cash injection, Niall Dickson, chief executive of the NHS Confederation, said the "failure" in care homes is "nothing short of a national disgrace".
"Care homes are where the major battle with Covid-19 is now raging and we have neglected it for too long.
"More money for infection control and the extra support from the NHS should alleviate some of the incredible pressure facing care homes now."
He welcomed the cash but said it needs to go where it's "most needed", with carers citing issues with "testing and PPE".
"When this is over, it will be time to tackle our collective failure to address social care, which is nothing short of a national disgrace," he added.
A Cabinet minister acknowledged the coronavirus crisis in care homes was “absolutely terrible”.
Communities Secretary Robert Jenrick told BBC Radio 5 Live: “I don’t deny that what is happening in care homes is absolutely terrible. It’s a huge challenge.
“But we are trying to put as much support as we can around care homes.”
At the government's daily coronavirus press conference he explained how the cash would be used.
Along with extra cash, the Government was trying to ensure staff and residents can get tested, he said.
“We are trying to help them to have the best possible infection control practices, we are trying to reduce the amount of rotation and movement of staff between care homes, which is one of the main reasons why the virus is spreading,” he added.
He said the most recent £600 million promised for homes in England was “to help the alleviate some of those challenges”.