"We can and must tackle mpox together," said Hans Kluge, WHO regional director for Europe, in a UN media briefing.
"So will we choose to put the systems in place to control and eliminate mpox globally? Or we will enter another cycle of panic and neglect? How we respond now and in the years to come will prove a critical test for Europe and the world," he added.
Mpox, a viral infection that causes pus-filled lesions and flu-like symptoms, is usually mild but can kill.
The clade 1b variety has caused global concern because it seems to spread more easily through routine close contact.
A case of the variant was confirmed last week in Sweden and linked to a growing outbreak in Africa, the first sign of its spread outside the continent.
The WHO declared the recent outbreak of the disease a public health emergency of international concern after the new variant was identified.