Naxals have put up banners inMaharashtra's Gadchiroli district calling for a bandh till May 22, police said on Thursday.The banners and leaflets, announcing a bandh till May 22, were put up at Kamlapur square in the district late on Wednesday night, an official said.Naxals have called for the district-wide bandh to condemn the death of woman rebel Srujjanakka, who was killed in a police encounter on May 1, he said.Meanwhile, naxals set fire to four trucks in the area on the intervening night of Tuesday and Wednesday, an official said.