Cases of monkeypox, which can cause puss-filled boils, are under "urgent investigation" in the UK.
Four cases were detected on Sunday that have no link to foreign travel, UK health authorities said.
Dr Susan Hopkins, UKHSA chief medical adviser, said the apparent spread of monkeypox was "unusual."
Monkeypox cases in the UK are under "urgent investigation" according to health officials, after four new cases were detected on Sunday.
A total of seven monkeypox cases were diagnosed in the UK between May 6 and May 15. After the first case was announed on 7 May, two additional patients not linked to that case were confirmed on May 14.
The latest four cases have no known connection with the previous confirmed cases. The individuals have the West Afrian clade of the virus, which is mild compared to the Central African Clade, according to the UK Health Security Agency
Monkeypox is a rare but potentially deadly illness. Its can cause include flu-like symptoms and puss-filled boils that cover the body. It doesn't tend to spread easily among people unless they're in close contact. Those infected usually have traveled to regions such as West Africa where the illness is most common.
The UKHSA said the four new cases had no link to travel to a country where monkeypox is endemic.
Susan Hopkins, chief medical adviser at UKHSA, said in a statement that evidence suggested there may be community transmission of monkeypox, "spread by close contact."
"This is rare and unusual," she said.
The UKHSA is studying sexual contact as a route of transmission as all four new monkeypox cases self-identified as gay, bisexual, or men who have sex with men.
"As the virus spreads through close contact, we are advising these groups to be alert to any unusual rashes or lesions on any part of their body, especially their genitalia, and to contact a sexual health service if they have concerns," the organization said.
"Exactly where and how they acquired their infections remains under urgent investigation, including whether they have further links to each other," it said.
The virus is not thought to be spread via sexual contact.
Jimmy Whitworth, a professor of international public health at London School of Hygiene & Tropical Medicine told the Science Media Center on Tuesday: "The most likely mode of spread in this cluster is through close contact: touching skin or bedding, or shared utensils. There is no need to postulate actual sexual transmission through genital or oral secretions."
Is monkeypox deadly?
According to the World Health Organization, the proportion of those diagnosed with monkeypox that die from it ranges from 1% to 10% depending on the strain of the virus they catch.
Dr. Michael Skinner, a reader in virology at Imperial College London, told the Science Media Center on Tuesday that most cases of monkeypox in the UK were likely to be the less deadly strain.
"The general public have no need for concern, but clinicians and public health authorities need to be on alert to spot infected cases early to limit transmission," he said.
The WHO said on Sunday that trade or travel restrictions to the UK or Nigeria weren't necessary.