Health officials in Florida are investigating three cases of Zika infection that were not linked to travel or the known zone of active mosquito transmission near downtown Miami.
The southern US state now has a total of 28 cases of Zika infection that are all believed to have been spread by local mosquitoes carrying the virus, which can cause serious birth defects.
‘The three non-travel related Zika cases reported in Florida - one in Palm Beach County to the north of Miami, and two in Miami-Dade.
There have also been 441 cases of Zika that were brought to Florida by people who were infected while traveling outside the United States.
State health authorities say they still believe the transmission is only occurring inside a one-square-mile (2.6-square-kilometer) area of the Wynwood neighborhood, north of downtown Miami.
But the health department said an "investigation is beginning" in another area of Miami-Dade County, which it did not identify.
Officials are probing three non-travel related cases, one in Palm Beach County to the north of Miami, and two in Miami-Dade.
"The department has not yet determined where the individual in Palm Beach County or the two individuals outside the one-square mile in Miami-Dade County likely contracted Zika and will share more details as the investigations progress," the Florida Department of Health said a statement.
"If the department finds evidence that active transmission is occurring in an area, we will notify the media and the public."
Florida is so far the only US state to report cases of local Zika transmission since the outbreak began sweeping Latin America last year.