At least 37 people have been killed and 36 others wounded after a hotel in the Tunisian coastal city of Sousse came under attack by unidentified gunmen.
Five British citizens and an Irish woman were confirmed to be among those killed in the mass shooting on Friday at the Mediterranean beach resort packed with holidaymakers.
UK Foreign Secretary Philip Hammond said a "high proportion" of those killed and wounded at the popular resort of Port el Kantaoui were expected to be British.
On his part, Irish Foreign Affairs Minister Charles Flanagan said in a statement: "Sadly, I can confirm that an Irish citizen has been killed in the attack in Sousse.
"In light of this incident we are changing our travel advice for Tunisia to 'exercise extreme caution'."
He told reporters that the victim was a woman, while Irish media reported that she was a nurse in her 50s with a son and a daughter.
One attacker was killed by police and a search operation was ongoing, with reports that another attacker was involved.
The attack was on the Imperial Marhaba hotel, local radio reported. Other reports indicated that two hotels may have been attacked.
Al Jazeera's Nazanine Moshiri, reporting from Tunis, said that local reports indicated that gunmen may have specifically targeted tourists at the resort - but that the reports have not yet been confirmed.
She said that the death toll was expected to rise.
Tunisia has been on high alert since March when gunmen attacked the Bardo museum in Tunis, killing a group of foreign tourists in one of the worst attacks in a decade in the North African country.
Our correspondent said that the new attack would be another blow to the country's economy, which relies heavily on tourism.
The attack was on the Imperial Marhaba hotel, local radio said [File]