A day after the convoy of Congress candidate Rajendra Pambhoi was attacked, leaving six policemen dead, Naxalites today planted landmines in Kanker and Dantewara districts of Chhattisgarh to stop the movement of polling parties and paramilitary forces, official sources said.Officials said that the administration is finding it difficult to get the landmines defused because police parties and experts get fired at if they try to clear them.Reports reaching Raipur said the Naxalites, who have given a call for boycott of the polls, have also positioned themselves in the interiors of Kanker districts to block the movement of polling parties.‘‘The Naxalites have planted landmines and are not letting the polling parties to move ahead. There was also an exchange of fire at one spot. Reinforcements have been sent there,’’ said K.K. Chakravarti, Chief Electoral Officer. He admitted Naxalites have created serious problems in Bastar, Kanker and Dantewara districts. If the police fail to get the routes cleared of the landmines, polling would not be possible in some of the interior polling stations.