Two new cases of monkeypox have been identified in the UK, bringing the latest total of confirmed infections to nine, the UK Health Security Agency said.
One person was reported to have the disease in London and another in the south-east of England, the agency said.
None of the infected people have travelled to countries where monkeypox is endemic, leading experts to say the new cases were caused by community transmission.
It means there have been nine cases reported since May 6 and recent cases identify as gay, bisexual or men who sleep with men (MSM).
But the two new cases have no links to the previous infections, the agency said.
The health agency is advising gay, bisexual and MSMs 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 through sex, but is not considered to be a sexually transmitted infection.
“These latest cases, together with reports of cases in countries across Europe, confirms our initial concerns that there could be a spread of monkeypox within our communities," said Dr Susan Hopkins, chief medical adviser at the agency.
“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.
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.
Most people recover from monkeypox within weeks, but the disease is fatal for up to 1 in 10 people, according to the World Health Organisation.
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.
US health officials on Thursday said they were looking into whether a new case of monkeypox in a man in Massachusetts could be linked to outbreaks in Europe.
Authorities said they were in contact with officials in the UK and Canada, which the man had recently visited, as part of the investigation.
But “at this point in time, we don’t have any information that links the Massachusetts case to cases in the UK”, said Jennifer McQuiston of the US Centres for Disease Control and Prevention (CDC).
She said while it is the only US case of which the CDC is aware, the authority is “preparing for the possibility of more cases”.
The US case poses no risk to the public and the Massachusetts resident has been admitted to hospital but is in good condition, officials said.