ISTANBUL — Turkish fighter jets, which on Friday attacked Islamic State targets in Syria, have launched a wave of airstrikes in northern Iraq, targeting camps of the militant Kurdistan Workers’ Party for the first time in four years, the prime minister’s office said Saturday.

The Iraq raids, which began late Friday and continued into Saturday, effectively ended an unstable two-year cease-fire between the Turkish government and the Kurdish militants, also known by the initials of their Kurdish name, P.K.K. After a three-decade conflict that claimed at least 40,000 lives, the two sides reached a fragile peace in 2013, though there have been a few minor clashes since then.

Fighter jets also struck Islamic State targets in Syria for a second day, Prime Minister Ahmet Davutoglu’s office said in the statement on Saturday. The jets entered Syrian airspace to do so, the statement said, unlike during the previous strikes, which the government said were carried out from the Turkish side of the border.

“No one should doubt our determination,” Mr. Davutoglu said, speaking to reporters in Ankara, the capital, on Saturday. “We will not allow Turkey to be turned into a lawless country.”