North Wales Police are investigating after a swastika was sprayed on a cenotaph on Remembrance Sunday in Buckley, Flintshire, in north Wales.
A neo-Nazi flag was also left at the monument at Hawkesbury Memorial Garden in the town, cops confirmed.
North Wales Police Inspector Iwan Jones said: "This was a distressing and distasteful hate crime on such an emotive weekend, and we will do all we can to identify those responsible.”
Buckley councillor David Ellis said: "A lot of hard work went in to restoring the memorial, and to see what happened to it on a day of commemoration is heartbreaking.
“The slogan painted on is the ultimate mark of disrespect to those who gave everything and made the ultimate sacrifice for us. I am absolutely devastated and so annoyed about what has happened.
“There is CCTV around the area and it will be checked by the police and I can only hope the culprits are caught and brought to justice.”
The memorial was refurbished just two years ago and an extra 36 names were added to it.
Councillor Ellis said Steve Blackwell, of Blackwell Memorials, is “working hard” to remove the symbol.
He said: "Steve is doing everything he can, and a huge thanks to him. But the memorial is made of York stone, which is very absorbent and the fact the paint has got into the wording of the names makes it very difficult to clean off.
"We had such a brilliant service on Sunday, and the people of Buckley turned out in their droves for it. What happened later in the day leaves a very sour taste."
Councillor Ellis said the town is planning additional security measures, such as locks on the gate to the memorial garden, to prevent further attacks.