Nurses have blamed Rishi Sunak for failing to agree a pay deal as they have announced two further strike dates next month.
In a massive escalation, walkouts will take place at a bigger number of hospitals than before.
Nurses will strike at 73 NHS trusts compared to 55 in January, the Royal College of Nursing announced.
Pat Cullen, the union's general secretary, said: “It is with a heavy heart that nursing staff are striking this week and again in three weeks. Rather than negotiate, Rishi Sunak has chosen strike action again.
“We are doing this in a desperate bid to get him and ministers to rescue the NHS. The only credible solution is to address the tens of thousands of unfiled jobs – patient care is suffering like never before.
“My olive branch to government – asking them to meet me halfway and begin negotiations – is still there. They should grab it.”
Industrial action will be held for 12 hours on both February 6 and 7 in England and Wales.
It follows walkouts due to take place tomorrow (WEDS) and on Thursday at NHS trusts that did not take part in industrial action last month.
The RCN union staged its first nationwide strikes in its 106-year history in December in an ongoing dispute over pay and working conditions.
The union previously demanded a 19% pay rise but earlier this month Ms Cullen said nurses could be ready to accept a 10% increase if Tory ministers finally open pay talks.
The RCN says low pay is pushing nursing staff out of the profession and contributing to record vacancies.
The new strike dates in February coincide with the tenth anniversary of the Robert Francis inquiry, which identified nurse staffing as an essential factor in patient safety and mortality rates.
NHS Providers interim chief Saffron Cordery said: “The announcement of two further nurse strike dates on consecutive days across more locations next month is very worrying.
“We’ve seen how disruptive these strikes can be, and more extensive industrial action is likely to have an even greater impact. Nobody wants this to continue happening.
“There are three weeks between now and these newly announced dates in February. This is more than enough time for the government and the unions to open negotiations on pay for 2022-23 and avert more strikes.”
The Prime Minister's spokesman said: "We would continue to urge unions to step back from strike action which will have an impact on patient care. We know that in the first round of strikes, 11,000 appointments were cancelled so it's inevitable this on a larger scale will have a larger impact.
"That is hugely regrettable at a time when the health service is under significant pressure.
"We feel there have been constructive talks with the unions and want those to continue rather than unions taking to the picket lines."
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