The Greek islands of Santorini, Serifos and Tinos have been added to Wales’s quarantine list.
People travelling to Wales from the islands must now self-isolate for 14 days from their arrival.
This is due to a “rising number” of coronavirus cases in these areas, the Welsh Government said.
Health Minister Vaughan Gething said he had made the decision after reviewing assessments by the Joint Biosecurity Centre (JBC).
The measure came into force at 4am on Wednesday.
Mr Gething has previously said that an “element” of coronavirus transmission in Wales is from people travelling back from Europe.
Wales has seen the highest number of positive Covid-19 cases in months and a local lockdown, expected to last until at least October, has come into force in Caerphilly.
On Tuesday, Public Health Wales reported that 150 people had tested positive for coronavirus, representing the highest daily figure since May 20.
There were no further deaths in people with the virus, with the total in Wales since the beginning of the pandemic remaining at 1,597.
Last Thursday, the Welsh Government introduced the measure for Portugal, Gibraltar, French Polynesia and six other Greek islands – Mykonos, Zakynthos, Lesbos, Paros, Antiparos and Crete.
Speaking at the time, Mr Gething said there has been a “rising tide of infections” from the Greek islands and the quarantine requirement is necessary to keep Wales safe.
And on Monday, the UK Government added the Greek islands of Crete, Lesbos, Mykonos, Santorini, Serifos, Tinos and Zakynthos to its quarantine list.
This forms part of the UK Government’s new regional approach to quarantine policy, in which islands can be added or removed from the quarantine list should infection rates differ from their mainland countries.