UK health officials said on Friday there had been 11 more confirmed cases of the rare monkeypox virus in the country, taking the total to 20.
The announcement came as France, Belgium and Germany reported their first cases of monkeypox, joining several other European and North American nations in detecting the disease, which is endemic in parts of Africa.
The UK Health Security Agency (UKHSA) said it had "detected 11 new cases of monkeypox in England", up from a total of nine.
"Most cases are mild and I can confirm we have procured further doses of vaccines that are effective against monkeypox," Health Secretary Sajid Javid tweeted.
The UKHSA's chief medical adviser, Susan Hopkins, said that she expected "this increase to continue in the coming days and for more cases to be identified in the wider community".
She particularly urged gay and bisexual men to look out for symptoms, saying a "notable proportion" of cases in UK and Europe came from this group.
The UKHSA said monkeypox had not previously been described as a sexually transmitted infection.
The World Health Organization (WHO) said it was also investigating the fact that many cases reported were people identifying as gay, bisexual or men who have sex with men.
Symptoms of the disease include fever, muscle aches, swollen lymph nodes, chills, exhaustion and a chickenpox-like rash on the hands and face.
It can be transmitted through contact with skin lesions and droplets of a contaminated person, as well as shared items such as bedding and towels.
The first UK case was announced on May 7, in a patient who had recently travelled to Nigeria.
Two more cases were reported a week later, in people in the same household. They had no link to the first case.
The UKHSA said that four further cases announced May 16 all identified as gay, bisexual or other men who have sex with men and appeared to have been infected in London.
It said two new cases reported on May 18 also had no history of travel to countries where the virus is endemic and "so it is possible they acquired the infection through community transmission".
It did not give any details of the latest cases of infection announced on Friday.
Cases of monkeypox have also been detected in Italy, Portugal, Spain and Sweden as well as in the United States and Canada, leading to fears that the disease -- normally concentrated in Central and West Africa -- may be spreading.
Monkeypox usually clears up after two to four weeks, according to the WHO. (AFP)