Israel and Switzerland are the latest countries to confirm cases of monkeypox, bringing the total number of nations reporting outbreaks to 14.
Both countries said they identified one infected person who had recently travelled, but Israel said it was investigating other suspected cases.
More than 80 cases have been confirmed in the recent outbreak in Europe, the US, Canada and Australia.
Monkeypox is most common in remote parts of Central and West Africa.
This outbreak has taken scientists by surprise, but monkeypox does not tend to spread easily between people and the risk to the wider public is said to be low.
The illness is usually mild and most people recover in a few weeks, according to the UK's National Health Service.
The World Health Organization has said another 50 suspected cases are being investigated - without naming the countries involved - and warned that more infections are likely to be confirmed.
Asked about the outbreak as he finished a visit to South Korea, US President Joe Biden said that if the virus were to spread more widely it would be "consequential", adding that "it is something that everybody should be concerned about".
He said the US was "working hard" on its response and what vaccines in might use.
After the outbreak was first identified in the UK, the virus began to be detected across Europe - with public health agencies in Spain, Portugal, Germany, Belgium, France, the Netherlands, Italy and Sweden all confirming cases.
Although there is no specific vaccine for monkeypox, several countries have said they are stocking up on smallpox vaccines, which are about 85% effective in preventing infection because the two viruses are quite similar.