It came as they held gave an update on Europe's COVID surge.
They warned that one-in-10 people in WHO's European region will have had a positive test for COVID-19 by the end of the week.
Even though 66.4% of people in European Union countries are fully vaccinated against the virus, many governments have imposed new measures on people who are unvaccinated in an effort to encourage more people to get the COVID-19 jab.
In Italy, a super health pass, proving vaccination or recovery, is needed to access cinemas and indoor dining, while in Germany, the unvaccinated are restricted from much of public life.
Austria, meanwhile, will mandate vaccinations from February 1 in order to encourage more people to get the jab.
But Dr Hans Kluge, the WHO regional director for Europe, said mandating vaccines should be a "last resort" and that countries must reach out to communities first.
"Mandates around vaccination are an absolute last resort and only applicable when all other feasible options to improve vaccination uptake have been exhausted," Kluge said.