A bench grinder was used to damage the war medals, which included the Pacific Star, the Defence Medal, the War Medal and the NZ War Service Medal.

A Blenheim man was so upset after being dumped by his girlfriend that he took a grinder to her great-grandfather's war medals.

The 26-year-old man admitted two charges of intentional damage at the Blenheim District Court on Monday.

A police summary of facts said the pair had been in a relationship for several months but the woman decided to leave him and moved out, taking some of her belongings.

The man sent his ex-girlfriend a Snapchat on February 28 which showed some of her clothes, her great-grandfather's war medals, and a bottle of lighter fluid, with the text "You just used and used me".

The medals were believed to be from World War II.

When she received the message, the woman was concerned he was going to damage the medals, and she and a friend went to the man's house to retrieve them.

They found the medals in the man's garden shed beside a bench grinder, some ripped from their ribbons, and some with parts ground off.

When spoken to by police, the man admitted burning some of his ex-girlfriend's clothes, but denied damaging the medals.

He did it because he was angry the woman had broken up with him, he told police.

The man was remanded on bail to April 18 for restorative justice, with bail conditions preventing him from contacting the woman or her friend.

His name was suppressed for 48 hours so he could inform his employer before his charges became public knowledge.