The stark warning comes after three Irish people and 30 Britons were killed when Islamist gunman Seifeddine Rezgui massacred tourists on a Sousse beach last month.
The British Foreign Office says it deems the threat from terrorist groups in the north African state to have ‘developed considerably’.
Ireland’s Department of Foreign Affairs said that it has noted the change in British officials advice and is urgently reviewing its own policy.
In a statement, it said: “The updated Foreign and Commonwealth Office travel advice on Tunisia has been noted.
“The Department is urgently reviewing its travel advice in consultation with the appropriate agencies.”
Its website warns: “In the light of the terrorist attack in Sousse, Tunisia, on 26 June 2015, the Department’s travel advice for Tunisia is to exercise extreme caution.
“While the Tunisian authorities have declared this incident to be over, we urge you to remain vigilant and to follow any instructions given by the police, tour operators, and hotel staff.”
Tour operators Thomas Cook, Thomson and First Choice tonight cancelled all bookings to Tunisia up until October 31st.
Thomas Cook said it plan to bring all customers in Tunisia back home as soon as possible using third party carriers and 10 scheduled flights over the weekend.
Thomson and First Choice said they have no holidaymakers in Tunisia, but is bringing back all staff from the country within the next 24 hours.
The Association of British Travel Agents urged people due to travel to Tunisia to contact the company they booked through.
It said: “For anyone due to travel, you should be aware that travelling out to Tunisia at this time is likely to invalidate your travel insurance policies. Most insurance policies will still provide cover for travellers in a country at the time of Foreign Office advice change.
“Those with holidays booked within the next 48 hours to Tunisia are advised to contact your travel company to discuss available options. If you have booked a package you will be entitled to a refund or alternative holiday.”
In updated travel advice, the British Foreign Office said: “Since the attack in Sousse, we have been working closely with the Tunisian authorities to investigate the attack and the wider threat from terrorist groups in Tunisia.
“Although we have had good co-operation from the Tunisian government, including putting in place additional security measures, the intelligence and threat picture has developed considerably, reinforcing our view that a further terrorist attack is highly likely.
“On balance, we do not believe the mitigation measures in place provide adequate protection for British tourists in Tunisia at the present time and we have therefore changed our travel advice accordingly.”
A Thomas Cook spokesman said: “As a result of the change in the Foreign & Commonwealth Office (FCO) advice to travel to Tunisia, Thomas Cook can confirm that it has cancelled all future bookings to Tunisia up until 31st October 2015.
“The safety and well-being of our customers is our primary concern. As always, we have been closely following the advice from the FCO and local authorities to monitor the situation in Tunisia.
“In response to the recent change in FCO advice we have taken this decision to bring all Thomas Cook customers back to the UK as soon as we can using third party carriers and on our 10 scheduled flights over the weekend.
“Thomas Cook is strongly advising its guests in the country to return on these flights. We are also sending our Specialist Assistance Teams to Tunisia to offer customers additional support in resort.
“We are committed to doing everything we can to support our guests in Tunisia at this time and will work to bring them back to the UK safely and as soon as possible.”
Thomson and First Choice spokesman said: “Customers due to travel to Tunisia up to and including 31 October will be given the opportunity to amend their holiday free of charge to any of our destinations currently on sale, or receive a full refund.
“Thomson and First Choice are also offering additional flights from airports across the UK to destinations including the Balearic Islands, Mainland Spain and Cyprus. In addition to customers being able to amend free of charge, those choosing these new flights will be offered a £50 discount per person.
“If customers wish to discuss their booking to Tunisia, they should visit the travel agent that they made their booking with or for holidays to Tunisia booked online customers should visit their local Thomson or First Choice store or call the customer service centre on 0800 009 3847 or 0203 636 1998 between 9am-9pm on Monday-Friday, 9am-8pm Saturday and 10am – 8pm Sunday.”
In the attacks last month three Irish people were among those killed.