Two additional cases of monkeypox have been identified in the UK – bringing the total to nine, according to the UK Health Security Agency.
One case was reported in London while another was found in south-east England, the UKHSA said.
Experts said it is possible the new cases were caused by community transmission because the individuals affected have no travel links to a country where monkeypox is endemic.
It means there have been nine cases reported since May 6 and recent cases self-identify as gay or bisexual men.
But the two new cases have no links to the previous six, the agency said.
The UKHSA is advising gay and bisexual men to check for any usual rashes or lesions on their bodies, particularly their genitals, and to contact a sexual health service if they are concerned.
Monkeypox can be passed on by direct contact though sex, but is not considered to be a sexually transmitted infection.
Dr Susan Hopkins, Chief Medical Adviser, UKHSA, said: “These latest cases, together with reports of cases in countries across Europe, confirms our initial concerns that there could be spread of monkeypox within our communities.
“UKHSA has quickly identified cases so far and we continue to rapidly investigate the source of these infections and raise awareness among healthcare professionals.
“We are particularly urging men who are gay and bisexual to be aware of any unusual rashes or lesions and to contact a sexual health service without delay if they have concerns. Please contact clinics ahead of your visit.
“We are contacting any identified close contacts of the cases to provide health information and advice.”
The health agency said the virus – which usually causes a mild illness – does not spread easily between people and the risk to the UK population remains low.
Undated handout image issued by the UK Health Security Agency of the stages of Monkeypox UK Health Security Agency
Anyone with concerns that they could be infected with monkeypox is advised to contact NHS 111 or a sexual health clinic, although they are urged to notify the clinic before attending.
The rash, which can develop as part of the virus, changes and goes through different stages before finally forming a scab, which later falls off.
The health agency also said that initial symptoms of monkeypox include fever, headache, muscle aches, backache, swollen lymph nodes, chills and exhaustion.
The first case was a person who had recently travelled to Nigeria, which is where they were believed to have contracted the infection, before travelling to the UK.
Close-up of monkeypox lesions on the arm and leg of a female child Wikicommons