AFP journalists on site a noted heavy police presence at the site of the 1941 Jedwabne massacre -- a former barn in which local Polish farmers locked up around 300 Jews, including women and children, before setting it on fire.Right next to the ceremony, about 1,000 people attended demonstrations and a Catholic mass organised by far-right parties, who refuse to acknowledge the responsibility of Polish villagers for the killings.Several participants in the commemoration were draped in Israeli and EU flags, as they paid their respects at a monument erected in 2001 to mark the site of the pogrom. Chief Rabbi of Poland Michael Schudrich called for unity as demonstrations carried on outdoors, inviting participants in the ceremony to read out together the names and occupations of Jews murdered in Jedwabne.Poles blamedAn official investigation confirmed in 2003 that the massacre had been carried out by Poles from Jedwabne, rather than by Nazi German occupiers. This stood in contrast to long-held historical narratives in Poland, and ultra-nationalist groups continue to challenge the investigation's findings. They argue that exhumations of the victims -- halted in 2001 for religious reasons at the request of the Jewish community -- must be resumed. "As long as we do not know the truth, there will be divisions," Elzbieta Rybarska, carrying a Polish flag, told AFP.