Cladding from three tower blocks in Newport has failed new safety tests.
Newport City Homes (NCH) said samples from the flats at Milton Court, Hillview and Greenwood had been tested.
It added that fire risk assessments were up to date and that it had already adopted relevant additional fire safety measures issued by government.
Swansea council said cladding used on those buildings had now passed what it described as a more comprehensive test.
The authority said the "whole system" test looked at fire resistance of the cladding system as a whole, including the panels, the mineral core, insulation and firebreaks.
Newport's social housing is run by NCH, whose chief executive Ceri Doyle said: "We have a dedicated presence at each of our tower blocks, alongside fire safety officers, so that residents can speak to someone if they have any questions or concerns.
"We are proceeding to conduct 'whole system' testing, however, our focus now is to reassure residents that the homes they live in are safe."
She added the tower blocks also have a number of fire safety measures in place including smoke and fire alarms, fire doors, fire retardant paint and evacuation routes.
Andy Thomas, assistant chief fire officer at South Wales Fire and Rescue Service, said it was working with NCH "to ensure the safety of residents in high-rise buildings".