The information was shared with AFP on Monday by the head of the organization’s European branch.
"It's going to get tougher. In October, November, we are going to see more mortality," WHO Europe Director Hans Kluge said.
More recently across the continent, there has been a significant uptick in the number of coronavirus cases although Covid-19 deaths in Europe have remained relatively stable.
The resurgence is however expected to lead to an increase in daily Covid-19 deaths, the WHO said.
"It's a moment where countries don't want to hear this bad news, and I understand," Kluge told AFP in an interview, stressing that he wanted to send the "positive message" that the pandemic "is going to finish, at one moment or another".
The WHO Europe's 55 member-states are holding an online meeting on Monday and Tuesday to discuss their response to the new coronavirus and agree on their overall five-year strategy.
However Kluge, based in Copenhagen, raised a warning finger to those who believe that the development of a vaccine will bring an end to the pandemic.
"I hear the whole time: 'the vaccine is going to be the end of the pandemic'. Of course not!," the Belgian said.