The three militants from the separatist Kurdistan Workers' Party (PKK) were killed in a clash in the mountainous region of Sason, the chief of staff said on his website.

In a separate incident, one security officer was killed and another injured in a landmine explosion planted by the PKK in the mountainous zone near the city of Semdinli, said the statement.

The Turkish army on Thursday discovered 144 kilogrammes (320 pounds) of explosives abandoned by a group of rebels as they were intercepted trying to cross illegally into Turkey from Syria.

The PKK -- listed as a terrorist organisation by Turkey, the European Union and the United States -- has been fighting since 1984 for the autonomy of the southeastern region, populated by a Kurdish majority.

The conflict has so far killed 37,000 people.

Turkish warplanes have staged air raids against PKK bases in northern Iraq since December, helped by US intelligence on rebel movements in the region.