An inscription reading “They were Flammable” and a Nazi swastika are seen in Jedwabne, Poland, Thursday, Sept. 1, 2011, on the monument dedicated to Jews from the town of Jedwabne burned to death by their Polish neighbors in 1941. - AP Photo

WARSAW: Poland on Thursday voiced outrage at the vandalism of a Holocaust memorial in the north of the country dedicated to Jews who were burned alive in a barn by their Polish neighbours during World War II.

Unknown perpetrators painted a green Nazi swastika on a stone monument in Jebwabne, where between 340 to 1,500 Polish Jews were killed in a July 10, 1941 massacre, perpetrated by Poles instigated by Nazi German occupiers, according to several historical accounts.

The vandals also wrote the words “I am not sorry for Jedwabne” and splattered green paint over a memorial plaque written in Hebrew.

“I wish to express my deep regret over the defacement of the monument in the town of Jedwabne commemorating the murder of Jews in 1941,” Foreign Minister Radoslaw Sikorski said in a Thursday statement.

Details of the massacre were first revealed in a 2001 book by historian Jan Tomasz Gross, and later supported by a Nazi and Communist-era crimes prosecutor.

Sikorski also condemned “several similar acts of hostility and vandalism directed against ethnic minorities in Poland.”

“There is no room for such behaviour in Polish society – even if it is the work of but a small group of extremists,” he added.

The Jebwabne incident is one of series of recent acts of vandalism against Poland's ethnic minorities.

Lithuanian language-versions of town names carved on large boulders were recently painted-over with the white and red of the Poland's flag.

Relations between the two communities have been strained over the rights of Lithuania's sizable Polish minority to use the Polish spelling of their names and bilingual public signs.

Some 28 road signs and a monument marking a Lithuanian theatre were all vandalised in the same way, according to local authorities.

The symbol of the Polish ultra-nationalistic right-wing Falanga organisation, dating from the 1930's, was also painted on the road signs and the monuments.

Unidentified individuals also attempted to burn down an Islamic centre in the eastern city of Bialystok and vandalised a historic synagogue in the village of Orla, also in Poland's east.

“I am convinced that the perpetrators will be swiftly tracked down and face the full extent of the law with regard to their actions,” Sikorski vowed Thursday.