NHS Providers interim chief executive Saffron Cordery said the announcement was “very worrying”.
“The health service is already stretched far too thin as trust leaders try to cope with ongoing industrial action alongside other mounting pressures bearing down on the NHS," she said.
“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.
“We understand how frustrated nurses feel, and how they have got to this point: below-inflation pay awards, the cost-of-living crisis, severe staff shortages and increasing workloads have created near-impossible conditions.
“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 2022-2023 and avert more strikes.”
Ambulance workers in the UK go on strike - in pictures
Nurses at 55 NHS trusts in England are scheduled to walk out on Wednesday and Thursday this week, but the February action from the RCN will cover 73 trusts.
About 12 health boards and organisations in Wales will also take part in the two consecutive days of strikes.
In December, thousands of nurses at trusts across England and Wales took part in two strike days, leading to the cancellation of thousands of hospital appointments and operations.
Meanwhile, the GMB held a meeting of its ambulance committee on Monday, and will announce the outcome on Wednesday.
It is likely that more strikes will be called in the dispute over pay and staffing.
RCN chief executive Pat Cullen said of the latest strike announcement: “It is with a heavy heart that nursing staff are striking this week and again in three weeks. Rather than negotiate, (Prime Minister) 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 unfilled jobs — patient care is suffering like never before.
“My olive branch to government — asking them to meet me half way and begin negotiations — is still there. They should grab it.”
Nurses strike in the UK - in pictures
The RCN has been calling for a pay rise at 5 per cent above inflation, although it has said it will accept a lower offer.
Inflation was running at 7.5 per cent when it submitted the 5 per cent figure to the independent pay review body in March.
But inflation has since soared, with RPI standing at 14.2 per cent in September.
Across the NHS, there are more than 130,000 staff vacancies.
“I hoped that the Welsh government would change their approach and come back to the table to negotiate with the RCN seriously on NHS pay and offer a substantive and restorative pay award. This has not happened to date," said Director of RCN Wales Helen Whyley.
“Their offer of a non-consolidated one-off payment, funded by monies ‘found down the back of the sofa’, shows the Welsh government’s disrespect for the crisis in the nursing workforce and a lack of a real commitment to want to address it.”
Winter strikes in Britain - in pictures
Downing Street urged union leaders to call off the action.
“We would continue to urge unions to step back from strike action, which will have an impact on patient care," said the prime minister’s official spokesman.
“We know in the first round of strikes 11,000 appointments were cancelled. So it’s inevitable that this, on a larger scale, will have a larger impact and that is hugely regrettable at a time when the health service is under significant pressure.
“We feel like there have been constructive talks with the unions and we’d want those to continue rather than taking to the picket lines.”
Its decision to strike on February 6 is designed to coincide with the 10th anniversary of the Robert Francis inquiry into Mid Staffordshire NHS Foundation Trust, which highlighted the effect of nurse shortages on patient care and excess deaths.
The inquiry uncovered the neglect of hundreds of patients at Stafford Hospital between 2005 and 2009, with accounts of some elderly people being left lying in their own urine, unable to eat, drink or take essential medication.
In a letter to the health secretary last week, Mr Francis and the Patients Association’s chief executive, Rachel Power, described the current stress on the NHS and excess death levels as “Mid Staffs playing out on a national level, if not worse”.
During the strike action, the health service will most likely run a bank holiday-style service in many areas.
UK nurses walk out for second time threatening further strikes in pay dispute - video
For the strikes this week, the RCN has agreed to still staff chemotherapy, emergency cancer services, dialysis, critical care units, neonatal and paediatric intensive care.
Some areas of mental health and learning disability and autism services are also exempt, while trusts will be told they can request staffing for specific clinical needs.
When it comes to adult A&E and urgent care, nurses will work Christmas Day-style rotas.
Last Wednesday, Health Secretary Steve Barclay said he does not “think it is right” to “retrospectively” go back to April when it comes to reviewing the current pay award for NHS staff.
It came after reports he is considering backdating any 2023-2024 pay rise, due to be finalised in the spring, to this month in order to boost the current year’s settlement offer.
Asked on BBC Radio 4’s Today programme if he is considering “reopening” the current year’s negotiations, Mr Barclay said it was not right to go back to April but suggested nothing was off the table.