Three soldiers have been killed during an anti-terror operation against the PKK in southeast Turkey on Sunday, a security source said.

The deaths took place in Mardin province's Nusaybin, a district on the Syrian border which has been the focus of counter-terrorism operations since March 14, according to a security source speaking on condition of anonymity due to restrictions on talking to the media.

On Saturday, Turkish Armed Forces confirmed that one of its soldiers was killed in Nusaybin district, adding that several terrorists in the southeast region were also killed on Friday. Six out of eight were killed in Nusaybin and two others were killed in Sirnak by Turkish security forces.

Explosives, illegal firearms and ammunition plus medical equipment were recovered.

Turkey's southeast has been the scene of significant military operations since late 2015, as the police and army seek to clear PKK terrorists from urban areas.

The PKK, listed as a terrorist organization by Turkey, the U.S. and EU, resumed its 30-year armed campaign against the Turkish state in July. Since then more than 400 members of the security forces have been killed and more than 3,700 PKK terrorists killed.