Cladding from three tower blocks in Newport have failed further fire safety tests carried out in the wake of the Grenfell Tower disaster.
Tests of the 11-storey blocks of flats at Milton Court, Hillview and Greenwood showed the wall systems "did not adequately resist the spread of fire".
The Building Research Establishment (BRE) tests said they were below the current building regulations guidance.
Newport City Homes says it is "focused" on "making sure residents are safe".
The Newport tower blocks are among more than 100 buildings that have failed the latest fire safety tests set up after the fire in London on June 14.
At least 80 people died in the Grenfell fire and the UK Government demanded urgent fire tests on all tower blocks.
Cladding at four Swansea tower blocks in Clyne Court, Sketty and Jefferys Court in Penlan, which initially failed tests, have been declared safe.
Milton Court in Ringland, Hillview in the Gaer and Greenwood in St Julian's were renovated in 2015 after being part of the £12.5m Welsh Housing Quality Standard investment programme.
But the flats in Newport have failed a "second large-scale test" of cladding including aluminium composite material (ACM) with mineral wool insulation, the only samples to have been sent from Welsh properties.
Rockwool, the makers of the insulation, said the test does not properly assess their product.
It is suspected that ACM panels on the outside of Grenfell Tower fuelled the spread of the fatal blaze, acting as kindling once the fire took hold.
Newport City homes are "working with independent experts on a programme of work to remove and replace the cladding" and install sprinkler systems.
"The safety of our residents has always and will continue to be a priority," said NCH executive director of operations Rob Lynbeck.
"At each of our tower blocks we're introducing fire wardens who will carry out frequent inspections of the building, throughout the day and night. They will make sure that escape routes are clear and monitor the safety of the building.
"The tower blocks have a number of fire safety measures already in place including: smoke/fire alarms; fire doors; fire breaks between every floor and vertically; fire retardant paint; two stairways that act as evacuation routes; and emergency lighting."
“Thank you very much BCC for the very impressive office refurbishment you have done for us. With experience in suspended ceilings and partitions your advice helped us to make the right choices for what we needed. The whole project was made very easy for myself.”
“We have used BCC a number of times and they deliver a very quick turn around but not sacrificing a very high standard of work. We will definitely continue to use BCC."