A Turkish Air Force F-16 fighter jet lands at Incirlik air base in Adana, Turkey, August 11, 2015. REUTERS/Murad Sezer - RTX1NXHJ

ANKARA (Reuters) - Turkish warplanes hit targets belonging to the Kurdistan Workers Party (PKK) in northern Iraq on Sunday, military sources said, as three soldiers and 12 militants were reported killed in separate clashes over the weekend.

The F-16 and F-4 2020 aircraft destroyed bunkers, ammunition depots and gun installations in four northern Iraqi regions, including Qandil, where the PKK has camps, the sources said.

The air strikes were launched early on Sunday and the aircraft returned safely to their bases, according to the sources.

Turkey has been regularly attacking PKK targets in mountainous northern Iraq since the collapse of a ceasefire between the PKK and the Turkish state in July last year.

It has also been clashing with militants across the largely Kurdish southeast of Turkey, which has seen some of the worst fighting since the height of the insurgency in the 1990s.

Three soldiers were killed on Sunday in a sweep of the city of Nusaybin in southeastern Mardin province, security sources said. They were searching a house when a home-made explosive went off, the sources said.

A day earlier, security forces killed a total of 12 militants in Mardin and the southeastern province of Sirnak, and in the eastern province on Tunceli, the military said in a statement.

Explosives were destroyed in those operations and 11 militants were arrested in Hakkari province, the military said.

More than 40,000 people have died since the autonomy-seeking PKK took up arms against the Turkish state in 1984. The group is considered a terrorist organization by Turkey, the United States and the European Union.