At least 13 policemen were killed on Tuesday after a police bus was hit by an improvised explosive device (IED) in Turkey's Igdir province.The bus was transporting a group of policemen to the Dilucu border gate, which connects Turkey to Azerbaijan’s Nakhichevan region, when it was hit near Hasanköy village, Hurriyet Daily News reported.Sources said the IED was planted by the outlawed Kurdistan Workers' Party (PKK) militants.In an earlier incident, a police bus en route to the Dilucu border gate had come under fire from PKK militants on August 27, leading to a clash with special forces. One policeman was injured in the clash.The latest PKK attack on security forces came two days after 16 Turkish soldiers were killed in an IED ambush in Hakkari.