FILE PHOTO: A woman holds a flag of the PKK (Kurdistan Workers' Party) during a demonstration against Turkish President Tayyip Erdogan in central Brussels, Belgium, November 17, 2016. REUTERS/Yves Herman/File Photo

ISTANBUL (Reuters) - Turkey will keep striking Kurdish PKK fighters in northern Iraq, the foreign ministry said on Saturday, a day after Baghdad formally complained that repeated Turkish air strikes violated its sovereignty and endangered civilians.

The Turkish military said on Friday it killed eight Kurdistan Workers Party (PKK) militants, prompting Iraqi authorities to summon the Turkish ambassador in Baghdad.

Turkey regularly hits PKK bases across its southern border, saying the militants use the remote and mountainous northern Iraqi region as a base for deadly attacks inside Turkey, where the outlawed group has waged an insurgency since the 1980s.

President Tayyip Erdogan threatened to launch a ground offensive in northern Iraq earlier this year. This week he also announced an imminent operation against a Kurdish militia in neighboring Syria.

The U.S.-backed YPG militia, which has been fighting Islamic State in Syria, controls Syria’s northeastern border with Turkey. Ankara says it is an extension of the PKK and poses a direct threat to Turkey.

“The activities of the PKK terrorist organization in the territory of Iraq and Syria have become a national security issue for Turkey,” Foreign Ministry spokesman Hami Aksoy said.

He said the government in Baghdad had a duty to prevent Iraqi land being used as a base for attacks on neighbors, and described Friday’s air strikes as an act of self-defense which Turkey carried out because Iraq would not act.

“These operations in the fight against terrorism will continue as long as terror organizations nest on Iraqi soil and as long as Turkey’s security needs require it to,” Aksoy said.

The PKK is designated a terrorist organization by Turkey, the United States and the European Union. It has waged a three-decade insurgency in Turkey’s largely Kurdish southeast that has killed about 40,000 people.