The Tánaiste has said he is "deeply troubled" by Turkey's fresh attacks on Syria.
Simon Coveney said the action risks undermining the progress made this year in the fight against Islamic State.
Turkey launched a military operation against Kurdish fighters in north-eastern Syria after US forces withdrew from the area.
Turkish president Recep Tayyip Erdogan announced the start of the campaign, which followed an announcement on Sunday by US president Donald Trump that American troops would step aside in a shift in US policy.
The Syrian Kurdish forces were long-time US allies in the fight against the so-called Islamic State group.
The Tánaiste said in a statement today that he was "deeply troubled" by the announcement.
"The fight against ISIS made decisive progress earlier this year," said Mr Coveney.
"Any unilateral military action against those groups which played a decisive frontline role in the fight against ISIS risks undermining this progress.
"Such action could also lead to further protracted instability and have serious humanitarian consequences. We urge Turkey to refrain from this action.
"While we understand Turkey’s security concerns about its own territory, unilateral military action cannot be condoned.
"The protection of civilians and respect for international humanitarian law must be paramount and any refugee returns must be voluntary, safe and dignified."