The chief executive of NHS England said repeated strikes by healthcare workers had made the workload “even more challenging”.
Amanda Pritchard said the ongoing strike action “clearly had an impact”.
Thousands of nurses across England will go on strike on Wednesday and Thursday, and around 1,000 ambulance staff in Wales will go on strike on Thursday.
Thousands of actions and appointments are expected to need to be canceled in the coming months, but Pritchard expressed hope that industrial action will be resolved.
“With the strike action going on for a long time and as these dates start to get closer, it does get more challenging, there’s absolutely no doubt about it,” she told BBC Radio 4’s Today program on Saturday. “It’s clearly having an impact. I think it’s obvious.”
“My sense is that everybody wants to try to reach a resolution,” she added.
Emergency services are under “alarming pressure” and more hospital beds are “desperately needed”, health leaders say.
Delays in hospital discharges are among the many pressures facing the NHS this winter, along with a shortage of beds, a new wave of Covid-19 infections, the worst flu season in a decade and ongoing strikes.
Monday 6 February could be the biggest strike action the NHS has ever seen since the United union announced a new strike for ambulance workers.
Thousands of nurses at the Royal College of Nursing (RCN) were due to strike on February 6-7, with the GMB union announcing earlier this week that its ambulance workers would join the strike on February 6.
On Friday, Unite said workers from five ambulance trusts in England and Wales would also take part in the February 6 strike.
Downing Street said the government remained willing to facilitate talks with unions, while acknowledging that the planned strikes would cause further “disruption” to patients.
Earlier this week, Health Minister Steve Barclay appeared to rule out a 10 per cent pay rise for nurses, speaking to broadcasters during a hospital visit.
“Well, 10% is unaffordable, it would be an extra £3.6bn a year and obviously it would tie up funding for patient services and given the backlog of the pandemic we need to invest in these essential services,” he said.
“Right now, within government, we have a whole-of-government approach — of course I’ve had discussions with the Treasury Department, as have other secretaries of state, and these things need to be balanced not only with the needs of teachers, education ministers, or trainers, but also traffic Minister, what can you afford? [the public] In terms of their own cost of living pressures. “
He insisted he was working “constructively” with the union but said he was “disappointed” by the strike.