Two policemen were shot dead by gunmen in the centre of the provincial capital Diyarbakir while a third was killed in Silopi in the neighbouring Sirnak province.
The source blamed the attack on Kurdistan Workers' Party (PKK) rebels who have been staging daily attacks against Turkish armed forces as the military keeps up air raids and operations against its strongholds in southeast Turkey as well as northern Iraq.
Three young Kurds from the youth wing of the PKK were meanwhile killed by security forces in Silopi, according to local officials.
Some 60 members of the Turkish security forces have been killed over the past five weeks as the PKK has hit back at a relentless government air and ground campaign, in the most significant losses sustained by the military and police in recent years.