Turkey targeted Kurdish militants in northern Syria and Iraq with a series of airstrikes on Sunday, days after a bombing attack killed six people in Istanbul. 

Military bases of the Kurdistan Workers’ Party, or PKK, and Syrian People’s Protection Units, or YPG, were hit in the attacks, Turkish Defense Minister Hulusi Akar said in a statement. 

"Shelters, bunkers, caves, tunnels and warehouses belonging to terrorists were destroyed with great success," Akar said. "The so-called headquarters of the terrorist organization were also hit and destroyed with direct hits."

Turkey airstrikes

A view shows the aftermath of airstrikes, which Turkey's defense ministry says it carried out, in Derik, Syria, November 20, 2022.    (North Press Agency/Handout via REUTERS)

Turkey airstrikes

People inspect a site damaged by Turkish airstrikes that hit an electricity station in the village of Taql Baql, in Hasakeh province, Syria, Sunday, Nov. 20, 2022. (AP Photo/Baderkhan Ahmad)

Turkish officials blamed the bombing in Istanbul, which killed six people and wounded dozens of others last Sunday, on the PKK and YPG. Both groups have denied involvement. 

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Turkish presidential spokesperson Ibrahim Kalin tweeted that "it's reckoning time for Istiklal," a reference to the avenue where the bombing took place. 

Bulgarian prosecutors have arrested five people involved in the bombing – three men of Moldovan origin, as well as a man and woman of Syrian Kurdish descent, according to Reuters. 

People leave the area after an explosion on Istanbul's popular pedestrian Istiklal Avenue Sunday, Istanbul, Sunday, Nov. 13, 2022.  (Ismail Coskun/IHA via AP)

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The PKK, which has been fighting an insurgency in Turkey since 1984, is considered a terrorist group by both Turkey and the United States, though the U.S. has allied with the YPG in the fight against ISIS in Syria. 

"We are determined, determined and able to save our country and our nation from the terror scourge that has plagued our country and our nation for 40 years," Akar said Sunday. 

The Associated Press contributed to this report.