Two of the soldiers were killed instantly when the device -- which the official said was planted by Kurdistan Workers' Party (PKK) fighters -- exploded in the city of Nusaybin as troops were trying to defuse it.

Another soldier who was badly injured later died of his wounds in hospital, the source told AFP.

The military has been battling for months against Kurdish fighters in Nusaybin, and eight PKK militants were killed there on Saturday, according to a military statement.

Turkish warplanes also hit PKK bases in northern Iraq overnight, destroying bunkers and weapons depots, the Anatolia news agency reported.

Fighting between Turkish security forces and the PKK, which is listed as a terrorist organisation by Ankara and its Western allies, erupted again last summer after the collapse of a two-year ceasefire.

Since then, hundreds of members of the Turkish security forces and several thousand Kurdish rebels have been killed.

In all, tens of thousands of people have been killed since the PKK took up arms in 1984 demanding a homeland for Turkey's biggest minority. Since then, the group has pared back its demands to focus on cultural rights and a measure of autonomy.