Australia and New Zealand warned Thursday that extremists may be planning an attack on the commemoration of a World War I campaign in Turkey this month.

Australian Veterans Affairs Minister Dan Tehan urged the nearly 500 Australians and New Zealanders registered to travel to Gallipoli, Turkey, to mark ANZAC Day April 25 to exercise a high degree of caution, but offered no specifics about the alleged threat. ANZAC Day is an annual holiday commemorating the April 25, 1915, landings in Gallipoli — the first major military action fought by the Australian and New Zealand Army Corps during World War I.

Australian Federal Police deputy commissioner Mike Phelan declined to release details of what prompted the warning, saying only that the government had received information that extremists may attack the services planned on the Gallipoli peninsula. Phelan said there was no specific plot linked to the alert.

“It is just that terrorists may indeed try to carry out a terrorist attack during the celebrations,” Phelan told reporters in the nation’s capital, Canberra. “That is all we have got at this stage.”

Tehan said Australia and New Zealand were working closely with Turkish authorities on security arrangements, but that the commemoration was scheduled to continue as planned.

For the past two years, Australian police have said they thwarted planned attacks on ANZAC Day celebrations in Australia. In 2015, police in Melbourne arrested five teenagers on suspicion of plotting an Islamic State group-inspired attack intended to coincide with the city’s ANZAC service. In 2016, police arrested a 16-year-old and charged him with planning an attack on an ANZAC ceremony in Sydney.

In a statement, New Zealand Foreign Minister Murray McCully urged New Zealanders in Turkey to be vigilant in public places and monitor the media for updates on potential safety risks.