A Holocaust survivors' group has condemned the desecration of a memorial in Poland to Jews murdered by Nazi collaborators.

The Jedwabne memorial marks the spot where hundreds of Polish Jews were burned alive in July 1941 by 40 of their countrymen.

They were sent into a barn and it was set alight. For decades the Nazis were held responsible, but after the publication a decade ago of a book on what happened, the Polish president acknowledged the massacre and made an official apology.

However this week police discovered that the memorial had been covered in graffiti. Vandals spraypainted the SS and swastika symbols and added the words "They were flammable" and "I don't apologise for Jedwabne".

The vandalism happened as Poland marked the 72nd anniversary of the country's invasion by Nazi forces, which started the Second World War.

Elan Steinberg, the vice-president of the American Gathering of Holocaust Survivors and their Descendants, called for the Polish authorities to punish the perpetrators of "this violent act of hate" as swiftly as possible.

Mr Steinberg said that the memorial's existence showed Poland's commitment to confronting its antisemitic past.

He said: "Coming on the anniversary of the Second World War, the target of the vandals' hatred was not only the Jewish community but the standing and reputation of modern-day Poland."

Commenting on the desecration of the Jedwabne Monument, Lord Greville Janner of Braunstone, Chairman of the Holocaust Educational Trust, said: "Jedwabne is a place where hundreds of innocent people were callously murdered. The desecration of the monument is a gross insult to the memory of those massacred there and all their descendents – and it is vital that those responsible are caught and brought to justice."